Cart

ABSTRACT

A cart may include a driving wheel, a motor configured to rotate the driving wheel, a motor drive circuit configured to drive the motor, a motor brake circuit configured to electrically brake the motor, a control device configured to control the motor via the motor drive circuit and the motor brake circuit so that a travelling speed of the cart becomes equal to or lower than an upper limit travelling speed, and a temperature sensor configured to detect a temperature of the motor brake circuit. The control device may be configured to change the upper limit travelling speed to a second upper limit travelling speed lower than the first upper limit travelling speed when the upper limit travelling speed is a first upper limit travelling speed and the temperature detected by the temperature sensor exceeds a first predetermined temperature.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese patent application No.2021-117078, filed on Jul. 15, 2021, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The art disclosed in the description herein relates to a cart.

BACKGROUND

Japanese Patent Application Publication No. H8-268286 describes a cart.This cart includes a driving wheel, a motor configured to rotate thedriving wheel, a motor drive circuit configured to drive the motor, amotor brake circuit configured to electrically brake the motor, and acontrol device configured to control the motor via the motor drivecircuit and the motor brake circuit so that a travelling speed of thecart becomes equal to or lower than an upper limit travelling speed.

SUMMARY

When the motor brake circuit is to electrically brake the motor, themotor brake circuit generates heat by a current that flows in the motorbrake circuit. If the motor brake circuit reaches an excessively hightemperature, the motor brake circuit is at a risk of not operatingnormally. The description herein provides an art that enables tosuppress a motor brake circuit of a cart from reaching an excessivelyhigh temperature.

A cart disclosed herein may comprise: a driving wheel; a motorconfigured to rotate the driving wheel; a motor drive circuit configuredto drive the motor; a motor brake circuit configured to electricallybrake the motor; a control device configured to control the motor viathe motor drive circuit and the motor brake circuit so that a travellingspeed of the cart becomes equal to or lower than an upper limittravelling speed; and a temperature sensor configured to detect atemperature of the motor brake circuit. When the upper limit travellingspeed is a first upper limit travelling speed and the temperaturedetected by the temperature sensor exceeds a first predeterminedtemperature, the control device may be configured to change the upperlimit travelling speed to a second upper limit travelling speed lowerthan the first upper limit travelling speed.

When a travelling speed of the cart becomes high, a generated heatquantity in the motor brake circuit upon braking the motor increases,and the temperature of the motor brake circuit becomes accordinglyhigher. According to the above configuration, the upper limit travellingspeed of the cart is reduced from the first upper limit travelling speedto the second upper limit travelling speed when the temperature of themotor brake circuit detected by the temperature sensor exceeds the firstpredetermined temperature. According to this, the generated heatquantity in the motor brake circuit upon braking the motor can bereduced. The motor brake circuit can be suppressed from reaching anexcessively high temperature.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view seeing a cart 2 of an embodiment from frontright upper side.

FIG. 2 is a perspective view seeing a carriage unit 4 of the embodimentfrom front right lower side.

FIG. 3 is a perspective view seeing the carriage unit 4 of theembodiment from rear right upper side,

FIG. 4 is a perspective view seeing a right front overload detectionmechanism 302 a of the carriage unit 4 of the embodiment from the frontright upper side.

FIG. 5 is a vertical cross-sectional view of the right front overloaddetection mechanism 302 a in a state Where an overload detection sensor320 a is in an off-state in the carriage unit 4 of the embodiment.

FIG. 6 is a vertical cross-sectional view of the right front overloaddetection mechanism 302 a in a state where the overload detection sensor320 a is in an on-state in the carriage unit 4 of the embodiment.

FIG. 7 is a vertical cross-sectional view of an overload detectionmechanism 364 in a state Where an overload detection sensor 380 is in anoff-state in a carriage unit 4 of a variant.

FIG. 8 is a vertical cross-sectional view of the overload detectionmechanism 364 in a state where the overload detection sensor 380 is inan on-state in the carriage unit 4 of the variant.

FIG. 9 is a cross-sectional view seeing the carriage unit 4 of theembodiment in a cross section along a front-rear direction and anup-down direction.

FIG. 10 is a cross-sectional view seeing the carriage unit 4 of theembodiment in a cross section along a left-right direction and theup-down direction.

FIG. 11 is a perspective view seeing a handle unit 8 of the embodimentfrom the rear right upper side.

FIG. 12 is a perspective view seeing a lower part of the handle unit 8of the embodiment from the front right lower side.

FIG. 13 is a perspective view seeing a support pipe 78, a clampingmember 80, a fixing member 82, a handle shaft 84, and a rotation anglesensor 88 of the handle unit 8 of the embodiment from the front rightlower side.

FIG. 14 is a perspective view seeing a movable cam member 90 of thehandle unit 8 of the embodiment from rear left upper side.

FIG. 15 is a perspective view seeing a fixed cam member 92 of the handleunit 8 of the embodiment from front left upper side.

FIG. 16 is a cross-sectional view seeing the lower part of the handleunit 8 of the embodiment in a cross section along the front-reardirection and the left-right direction in a state where an operation ofsteering rightward is performed on the handle unit 8.

FIG. 17 is a perspective view seeing the lower part of the handle unit 8of the embodiment from the front right lower side in a state where theoperation of steering rightward is performed on the handle unit 8.

FIG. 18 is a perspective view seeing a steering unit 10 and a frontwheel unit 12 of the embodiment from the front left upper side.

FIG. 19 is a perspective view seeing the steering unit 10 of theembodiment from the front left upper side.

FIG. 20 is a cross-sectional view seeing the steering unit 10 of theembodiment in a cross section along the front-rear direction and theleft-right direction.

FIG. 21 is a disassembled perspective view seeing a spindle 178, a camwheel 180, a movable gear 182, and a coil spring 184 of the steeringunit 10 of the embodiment from the rear left lower side.

FIG. 22 is a cross-sectional view seeing the steering unit 10 of theembodiment in a cross section along the front-rear direction and theup-down direction.

FIG. 23 is a perspective view seeing a right front wheel unit 12 a ofthe embodiment from the front left upper side.

FIG. 24 is a cross-sectional view seeing the right front wheel unit 12 aof the embodiment in a cross section along the left-right direction andthe up-down direction.

FIG. 25 is a perspective view seeing a rear wheel unit 14 of theembodiment from the rear right upper side.

FIG. 26 is a perspective view seeing a right rear wheel unit 14 a of theembodiment from the rear left upper side.

FIG. 27 is a perspective view seeing a bumper unit 16 of the embodimentfrom the front right upper side.

FIG. 28 is a cross-sectional view seeing a vicinity of a linear motionbearing 522 of the bumper unit 16 of the embodiment in a cross sectionalong the front-rear direction and the left-right direction.

FIG. 29 is a perspective cross-sectional view seeing the bumper unit 16of the embodiment from the rear left upper side.

FIG. 30 is a diagram schematically showing a circuit configuration ofthe cart 2 of the embodiment.

FIG. 31 is a diagram schematically showing a circuit configuration of aswitch circuit 436 of the embodiment.

FIG. 32 is a diagram schematically showing circuit configurations of ashutoff circuit 438, motor drivers 454, 456, 458, 460, and brakecircuits 468, 470, 472, 474 of the embodiment.

FIG. 33 is a diagram schematically showing a circuit configuration of ashutoff circuit 440 and electromagnetic brake drivers 464, 466 of theembodiment.

FIG. 34 is a diagram schematically showing a circuit configuration of ashutoff circuit 442 and a motor driver 462 of the embodiment.

FIG. 35 is a flowchart of processes executed by a main MCU 434 of thecart 2 of the embodiment.

FIG. 36 is a flowchart of processes executed by the main MCU 434 of thecart 2 of the embodiment in a manual mode.

FIG. 37 is a flowchart of processes executed by the main MCU 434 of thecart 2 of the embodiment in an automatic mode.

FIG. 38 is a flowchart of processes executed by motor MCUs 444, 446 ofthe cart 2 of the embodiment.

FIG. 39 is a flowchart of processes executed by the motor MCUs 444, 446of the cart 2 of the embodiment.

FIG. 40 is a flowchart of processes executed by motor MCUs 448, 450 ofthe cart 2 of the embodiment.

FIG. 41 is a flowchart of processes executed by the motor MCUs 448, 450of the cart 2 of the embodiment.

FIG. 42 is a graph showing chronological changes in a travelling speed,a brake current, and a brake circuit temperature in a case where thecart 2 of the embodiment travels on flatland and downhill in the manualmode.

FIG. 43 is a flowchart of processes executed by a motor MCU 452 of thecart 2 of the embodiment.

DETAILED DESCRIPTION

Representative, non-limiting examples of the present disclosure will nowbe described in thither detail with reference to the attached drawings.This detailed description is merely intended to teach a person of skillin the art further details for practicing aspects of the presentteachings and is not intended to limit the scope of the presentdisclosure. Furthermore, each of the additional features and teachingsdisclosed below may be utilized separately or in conjunction with otherfeatures and teachings to provide improved carts, as well as methods forusing and manufacturing the same.

Moreover, combinations of features and steps disclosed in the followingdetailed description may not be necessary to practice the presentdisclosure in the broadest sense, and are instead taught merely toparticularly describe representative examples of the present disclosure.Furthermore, various features of the above-described and below-describedrepresentative examples, as well as the various independent anddependent claims, may be combined in ways that are not specifically andexplicitly enumerated in order to provide additional useful embodimentsof the present teachings.

All features disclosed in the description and/or the claims are intendedto be disclosed separately and independently from each other for thepurpose of original written disclosure, as well as for the purpose ofrestricting the claimed subject matter, independent of the compositionsof the features in the embodiments and/or the claims. In addition, allvalue ranges or indications of groups of entities are intended todisclose every possible intermediate value or intermediate entity forthe purpose of original written disclosure, as well as for the purposeof restricting the claimed subject matter.

In one or more embodiments, a cart may comprise: a driving wheel; amotor configured to rotate the driving wheel; a motor drive circuitconfigured to drive the motor; a motor brake circuit configured toelectrically brake the motor; a control device configured to control themotor via the motor drive circuit and the motor brake circuit so that atravelling speed of the cart becomes equal to or lower than an upperlimit travelling speed; and a temperature sensor configured to detect atemperature of the motor brake circuit. When the upper limit travellingspeed is a first upper limit travelling speed and the temperaturedetected by the temperature sensor exceeds a first predeterminedtemperature, the control device may be configured to change the upperlimit travelling speed to a second upper limit travelling speed lowerthan the first upper limit travelling speed.

When the travelling speed of the cart becomes high, a generated heatquantity in the motor brake circuit upon braking the motor increases,and the temperature of the motor brake circuit becomes accordinglyhigher. According to the above configuration, the upper limit travellingspeed of the cart is changed from the first upper limit travelling speedto the second upper limit travelling speed when the temperature of themotor brake circuit detected by the temperature sensor exceeds the firstpredetermined temperature, by which the generated heat quantity in themotor brake circuit upon braking the motor can be reduced. Thus, themotor brake circuit can be suppressed from reaching an excessively hightemperature.

In one or more embodiments, when the temperature detected by thetemperature sensor becomes lower than a second predetermined temperaturelower than the first predetermined temperature after the upper hunttravelling speed has been changed from the first upper limit travellingspeed to the second upper limit travelling speed, the control device maybe configured to set the upper limit travelling speed back to the firstupper limit travelling speed.

According to the above configuration, after the motor brake circuitreaches a high temperature and the upper limit travelling speed is thusreduced, the upper travelling speed is not set back to its originalspeed until the motor brake circuit is sufficiently cooled, thus theupper limit travelling speed can be suppressed from frequently beingincreased and reduced.

In one or more embodiments, the cart may further comprise an operationmember for receiving an operation by a user. The cart may be configuredto operate in a manual mode and an automatic mode, wherein in the manualmode, the motor is driven when the operation member is on and the motoris stopped when the operation member is off, and in the automatic mode,the motor is driven regardless of whether the operation member is on oroff. Even when the temperature detected by the temperature sensorbecomes lower than the second predetermined temperature after the upperlimit travelling speed has been changed from the first upper limittravelling speed to the second upper limit travelling speed, the controldevice may be configured not to set the upper limit travelling speedback to the first upper limit travelling speed if an operation mode ofthe cart is the automatic mode.

If the cart is operating in the automatic mode when the motor brakecircuit is cooled sufficiently and the upper limit travelling speed isto be set back the first, upper limit travelling speed from the secondupper limit travelling speed, there is a risk that the cart suddenlyaccelerates. According to the above configuration, after the motor brakecircuit reaches a high temperature and the upper limit travelling speedis thus reduced, the upper limit travelling speed is not set back to itsoriginal speed even if the motor brake circuit is cooled sufficiently ifthe operation mode of the cart is the automatic mode. Thus, the cart canbe suppressed from suddenly accelerating.

In one or more embodiments, even when the temperature detected by thetemperature sensor becomes lower than the second predeterminedtemperature and the operation mode of the cart is not the automatic modeafter the upper limit travelling speed has been changed from the firstupper limit travelling speed to the second upper limit travelling speed,the control device may be configured not to set the upper limittravelling speed back to the first upper limit travelling speed if thecart is not stopped.

Even when the motor brake circuit is cooled sufficiently and theoperation mode of the cart is not the automatic mode, there is a riskthat the cart suddenly accelerates if the cart is not stopped uponsetting the upper limit travelling speed back to the first upper limittravelling speed from the second upper limit travelling speed. Accordingto the above configuration, after the motor brake circuit reaches a hightemperature and the upper limit travelling speed is thus reduced, theupper limit travelling speed is not set back to its original speed untilthe cart is stopped even when the motor brake circuit is cooledsufficiently and the operation mode of the cart is not the automaticmode, thus the cart can be suppressed from suddenly accelerating.

In one or more embodiments, even when the temperature detected by thetemperature sensor becomes lower than the second predeterminedtemperature after the upper limit travelling speed has been changed fromthe first upper limit travelling speed to the second upper limittravelling speed, the control device may be configured not to set theupper limit travelling speed back to the first upper limit travellingspeed if the cart is not stopped.

When the motor brake circuit is cooled sufficiently and the upper limittravelling speed is to be set back to the first upper limit travellingspeed from the second upper limit travelling speed, there is a risk thatthe cart suddenly accelerates if the cart is not stopped. According tothe above configuration, after the motor brake circuit reaches a hightemperature and the upper limit travelling speed is thus reduced, theupper limit travelling speed is not set back to its original speed evenif the motor brake circuit is cooled sufficiently until the cart isstopped. Thus, the cart can be suppressed from suddenly accelerating.

In one or more embodiments, the cart may further comprise an operationmember for receiving an operation by a user. The cart may be configuredto operate in a manual mode and an automatic mode, wherein in the manualmode, the motor is driven when the operation member is on and the motoris stopped when the operation member is off, and in the automatic mode,the motor is driven regardless of whether the operation member is on oroff. After the upper limit travelling speed has been changed from thefirst upper limit travelling speed to the second upper limit travellingspeed, the control device may be configured to set the upper limittravelling speed back to the first upper limit travelling speed if anoperation mode of the cart is not the automatic mode.

When the upper limit travelling speed is to be set back to the firstupper limit travelling speed from the second upper limit travellingspeed, there is a risk that the cart suddenly accelerates if the cart isoperating in the automatic mode. According to the above configuration,after the motor brake circuit reaches a high temperature and the upperlimit travelling speed is thus reduced, the upper limit travelling speedis not set back to its original speed if the operation mode of the cartis the automatic mode. Thus, the cart can be suppressed from suddenlyaccelerating.

In one or more embodiments, even when the operation mode of the cart isnot the automatic mode after the upper limit travelling speed has beenchanged from the first upper limit travelling speed to the second upperlimit travelling speed, the control device may be configured not to setthe upper limit travelling speed back to the first upper limittravelling speed if the cart is not stopped.

Even when the operation mode of the cart is not the automatic mode, ifthe cart is not stopped upon setting the upper limit travelling speedback to the first upper limit travelling speed from the second upperlimit travelling speed, there is a risk that the cart suddenlyaccelerates. According to the above configuration, after the motor brakecircuit reaches a high temperature and the upper limit travelling speedis thus reduced, upper limit travelling speed is not set back to itsoriginal speed until the cart is stopped even if the operation mode ofthe cart is not the automatic mode. Thus, the cart can be suppressedfrom suddenly accelerating.

In one or more embodiments, after the upper limit travelling speed hasbeen changed from the first upper limit travelling speed to the secondupper limit travelling speed, the control device may be configured toset the upper limit travelling speed back to the first upper limittravelling speed if the cart is stopped.

If the cart is not stopped upon setting the upper limit travelling speedback to the first upper limit travelling speed from the second upperlimit travelling speed, there is a risk that the cart suddenlyaccelerates. According to the above configuration, after the motor brakecircuit reaches a high temperature and the upper limit travelling speedis thus reduced, the upper limit travelling speed is not set back to itsoriginal speed until the cart is stopped. Thus the cart can besuppressed from suddenly accelerating.

In one or more embodiments, the cart may further comprise: a seconddriving wheel; a second motor configured to rotate the second driving asecond motor drive circuit configured to drive the second motor; asecond motor brake circuit configured to electrically brake the secondmotor; and a second temperature sensor configured to detect atemperature of the second motor brake circuit. The control device may beconfigured to control the second motor via the second motor drivecircuit and the second motor brake circuit so that a travelling speed ofthe cart becomes equal to or lower than the upper limit travellingspeed. When the upper limit travelling speed is the first upper limittravelling speed and the temperature detected by the second temperaturesensor exceeds the first predetermined temperature, the control devicemay be configured to change the upper limit travelling speed to thesecond upper limit travelling speed.

According to the above configuration, by reducing the upper limittravelling speed of the cart from the first upper limit travelling speedto the second upper limit travelling speed when at least one of themotor brake circuit and the second motor brake circuit exceeds the firstpredetermined temperature, generated heat quantities in the motor brakecircuit and the second motor brake circuit upon braking the motor andthe second motor can respectively be reduced. Thus, the motor brakecircuit and the second motor brake circuit can be suppressed fromreaching an excessively high temperature.

In one or more embodiments, the cart may further comprise a coolerconfigured to cool the motor brake circuit. The cooler may be configuredto continue cooling the motor brake circuit even after the motor hasstopped.

According to the above configuration, since the motor brake circuit canbe cooled by the cooler even while the motor is stopped, the motor brakecircuit can be cooled sufficiently, by which the motor brake circuit canbe suppressed from reaching an excessively high temperature when thecart operates thereafter.

In one or more embodiments, the motor brake circuit may be configured toelectrically brake the motor for 15 minutes or more.

According to the above configuration, braking on the motor by the motorbrake circuit can be continued over a long period of time, and theoperation of the cart can further be stabilized.

In one or more embodiments, the upper limit travelling speed may bewithin a range from 0 km/h to 10 km/h.

According to the above configuration, the cart can be suppressed fromtravelling at an excessively high speed, and travelling safety for thecart can be increased.

EMBODIMENTS

A cart 2 shown in FIG. 1 comprises a carriage unit 4, a luggage carrierunit 6, a handle unit 8, a steering unit 10, a front wheel unit 12, arear wheel unit 14, and a bumper unit 16. The cart 2 is configured tocarry objects placed on the luggage carrier unit 6. The cart 2 comprisesa receiver (not shown) installed in the carriage unit 4. The cart 2 isconfigured to operate in either a manual mode, an automatic mode, or aparking; mode. In the manual mode, the cart 2 is configured to moveforward or backward in accordance with an operation by a user in a statewhere the user standing behind the handle unit 8 is holding the handleunit 8. In the automatic mode, the cart 2 is configured to move bytracking a beacon (not shown) which the user standing in front of thecarriage unit 4 is holding, or execute a remote control operation ofmoving in accordance with instructions from a remote controller (notshown) which the user operates. In this case, the cart 2 receives radiowaves from the beacon or the remote controller by the receiver. In theparking mode, the cart 2 is configured to lock the rear wheel unit 14and stay parked on spot.

(Carriage Unit 4)

As shown in FIGS. 2 and 3 , the carriage unit 4 comprises a base plate20, a front support member 22, a rear support member 24, a right lowerframe 26, a left lower frame 28, a right upper frame 30, a left upperframe 32, a battery box 34, an overload detection mechanism 302, anemergency stop switch casing 304, an upper controller casing 306, and alower controller casing 36. The overload detection mechanism 302comprises a right front overload detection mechanism 302 a, a left frontoverload detection mechanism 302 b, a right rear overload detectionmechanism 302 c, and a left rear overload detection mechanism 302 d.

As shown in FIG. 2 , the base plate 20 is a member constituted ofaluminum, and has a substantially rectangular flat plate shape havingits longitudinal direction along a front-rear direction and its shortdirection along the left-right direction. The emergency stop switchcasing 304 is a member constituted of resin, and is fixed to a lowersurface of the base plate 20 at a front end of the base plate 20. Anemergency stop switch 308 which the user can operate by pressing thesame is arranged on a front surface of the emergency stop switch casing304. The emergency stop switch 308 is normally off, and turns on when itis press-operated by the user. The emergency stop switch 308 iselectrically connected to a main control circuit hoard. 44 to bedescribed later. The emergency stop switch casing 304 may be arranged ata rear, right, or left end of the base plate 20, and the emergency stopswitch 308 may be arranged on a rear, right, or left surface of theemergency stop switch casing 304 in accordance with the arrangementthereof.

The front support member 22 is a member constituted of steel, and isattached to the lower surface of the base plate 20 via the right frontoverload detection mechanism 302 a and the left front overload detectionmechanism 302 b at a front portion of the base plate 20. As shown inFIG. 3 , the rear support member 24 is a member constituted of steel,and is attached to the lower surface of the base plate 20 via the rightrear overload detection mechanism 302 c and the left rear overloaddetection mechanism 302 d at a rear portion of the base plate 20. Theright lower frame 26 and the left lower frame 28 are both membersconstituted of steel, and each extend in a front-rear direction belowthe base plate 20. A front portion of the right lower frame 26 and afront portion of the left lower frame 28 are each fixed to the frontsupport member 22. A rear portion of the right lower frame 26 and a rearportion of the left lower frame 28 are each fixed to the rear supportmember 24.

The right front overload detection mechanism 302 a, the left frontoverload detection mechanism 302 b, the right rear overload detectionmechanism 302 c, and the left rear overload detection mechanism 302 dhave same configuration as one another, which will collectively beexplained (for the configuration of one of the overload detectionmechanisms). As shown in FIG. 4 , the right front overload detectionmechanism 302 a, the left front overload detection mechanism 302 b, theright rear overload detection mechanism 302 c, and the left rearoverload detection mechanism 302 d each comprises a pillar member 312 a,312 b, 312 c, 312 d, a coil spring 314 a, 314 b, 314 c, 314 d, adetection plate 316 a, 316 b, 316 c, 316 d, a base member 318 a, 318 b,318 c, 318 d, and an overload detection sensor 320 a, 320 b, 320 c, 320d. As shown in FIG. 5 , the pillar member 312 a, 312 b, 312 c, 312 dincludes a circular column 322 a, 322 b, 322 c, 322 d, a flange 324 a,324 b, 324 c, 324 d, an upper small-diameter portion 326 a, 326 b, 326c, 326 d, and a lower small-diameter portion 328 a, 328 b, 328 c, 328 d.The circular column 322 a, 322 b, 322 c, 322 d has a substantiallycircular column shape of which axial direction extends along an up-downdirection. The flange 324 a, 324 b, 324 c, 324 d is arranged above thecircular column 322 a, 322 b, 322 c, 322 d, and has a shape protrudingradially outward than the circular column 322 a, 322 b, 322 c, 322 d.The upper small-diameter portion 326 a, 326 b, 326 c, 326 d is arrangedabove the flange 324 a, 324 b, 324 c, 324 d, and has a substantiallyround columnar shape with a smaller diameter than the circular column322 a, 322 b, 322 c, 322 d. The lower small-diameter portion 328 a, 328b, 328 c, 328 d is arranged below the circular column 322 a. 322 b, 322c, 322 d, and has a substantially round columnar shape with a smallerdiameter than the circular column 322 a, 322 b, 322 c, 322 d.

The upper small-diameter portion 326 a, 326 b, 326 c, 326 d is insertedfrom below into a through hole 330 a, 330 b, 330 c, 330 d defined in thebase plate 20. A threaded hole 332 a, 332 b, 332 c, 332 d is defined atan upper end of the pillar member 312 a, 312 b, 312 c, 312 d. A bolt 336a, 336 b, 336 c, 336 d is screw-fitted in the threaded hole 332 a, 332b, 332 c, 332 d via a washer 334 a, 334 b, 334 c, 334 d. In a statewhere the bolt 336 a, 336 b, 336 c, 336 d is screw-fitted in thethreaded hole 332 a, 332 b, 332 c, 332 d, the base plate 20 is heldbetween the washer 334 a, 334 b, 334 c, 334 d and the flange 324 a, 324b, 324 c, 324 d. Since an inner diameter of the through hole 20 a, 20 b,20 c, 20 d is slightly larger than an outer diameter of the uppersmall-diameter portion 326 a, 326 b, 326 c, 326 d, the pillar member 312a, 312 b, 312 c, 312 d is allowed to slightly tilt relative to the baseplate 20.

The lower small-diameter portion 328 a, 328 b, 328 c, 328 d is insertedfrom above into a through hole 338 a, 338 b, 338 c, 338 d defined in thefront support member 22 (or the rear support member 24). Since an innerdiameter of the through hole 338 a, 338 b, 338 c, 338 d is slightlylarger than an outer diameter of the lower small-diameter portion 328 a,328 b, 328 c, 328 d, the pillar member 312 a, 312 b, 312 c, 312 d isallowed to slightly tilt relative to the front support member 22 (or therear support member 24). The coil spring 314 a, 314 b, 314 c, 314 d isattached to the pillar member 312 a, 312 b, 312 c, 312 d. An upper endof the coil spring 314 a, 314 b, 314 c, 314 d abuts a lower surface ofthe washer 340 a, 340 b, 340 c, 340 d. An upper surface of the washer340 a, 340 b, 340 c, 340 d abuts a lower surface of the flange 324 a,324 b, 324 c, 324 d. A lower end of the coil spring 314 a, 314 b, 314 c,314 d abuts an upper surface of the front support member 22 (or the rearsupport member 24). The coil spring 314 a, 314 b, 314 c, 314 d biasesthe pillar member 312 a, 312 b, 312 c, 312 d upward relative to thefront support member 22 (or the rear support member 24).

A threaded hole 342 a, 342 b, 342 c, 342 d is defined at a lower end ofthe pillar member 312 a, 312 b, 312 c, 312 d. A bolt 344 a, 344 b, 344c, 344 d is screw-fitted in the threaded hole 342 a, 342 b, 342 c, 342 dvia the detection plate 316 a, 316 b, 316 c, 316 d. The detection plate316 a, 316 b, 316 c, 316 d includes a support portion 346 a, 346 b, 346c, 346 d having a substantially flat plate shape along the front-reardirection and the left-right direction, and a detection portion 348 a,348 b, 348 c, 348 d bent downward from an end of the support portion 346a, 346 b, 346 c, 346 d and having a substantially flat plate shape alongthe front-rear direction and the up-down direction.

The base member 318 a, 318 b, 318 c, 318 d includes an engagementportion 350 a, 350 b, 350 c, 350 d, a nut 352 a, 352 b, 352 c, 352 d, aguide portion 354 a, 354 b, 354 c, 354 d, and a sensor holder portion356 a, 356 b, 356 c, 356 d. The engagement portion 350 a, 350 b, 350 c,350 d is configured to engage with the front support member 22 (or therear support member 24). A bolt 358 a, 358 b, 358 c, 358 d isscrew-fitted in the nut 352 a, 352 b, 352 c, 352 d. A lower end of thebolt 358 a, 358 b, 358 c, 358 d penetrates the nut 352 a, 352 b, 352 c,352 d and abuts an upper surface of the front support member 22 (or therear support member 24). The base member 318 a, 318 b, 318 c, 318 d isfixed to the front support member 22 (or the rear support member 24) bytightening the bolt 358 a, 358 b, 358 c, 358 d relative to the nut 352a, 352 b, 352 c, 352 d in a state of having the engagement portion 350a, 350 b, 350 c, 350 d engaged with the front support member 22 (or therear support member 24). The guide portion 354 a, 354 b, 354 c, 354 dhas a shape for guiding movement of the detection plate 316 a, 316 b,316 c, 316 d in the up-down direction. The overload detection sensor 320a, 320 b, 320 c, 320 d is attached to the sensor holder portion 356 a,356 b, 356 c, 356 d. A position along the up-down direction forattaching the overload detection sensor 320 a, 320 b, 320 c, 320 d tothe sensor holder portion 356 a, 356 b, 356 c, 356 d is configuredadjustable.

The overload detection sensor 320 a, 320 b, 320 c, 320 d of the presentembodiment is a so-called photo interrupter. The overload detectionsensor 320 a, 320 b, 320 c, 320 d includes a light emitting element 360a, 360 b, 360 c, 360 d and a light receiving element 362 a, 362 b, 362c, 362 d arranged to face each other. The overload detection sensor 320a, 320 b, 320 c, 320 d is in an, off-state when the light emittingelement 360 a, 360 b, 360 c, 360 d is not blocked from the lightreceiving element 362 a, 362 b, 362 c, 362 d and is in an on-state whenthe emitting element 360 a, 360 b, 360 c, 360 d is blocked from thelight receiving element 362 a, 362 b, 362 c, 362 d. The overloaddetection sensor 320 a, 320 b, 320 c, 320 d is electrically connected tothe main control circuit board 44 to be described later (see FIG. 9 ).

As shown in FIG. 5 , in a state where no object is placed on the luggagecarrier unit 6 and thus a load from the luggage carrier unit 6 is notapplied to the base plate 20, an upper surface of the support portion346 a, 346 b, 346 c, 346 d of the detection plate 316 a, 316 b, 316 c,316 d abuts the lower surface of the front support member 22 (or therear support member 24) by a biasing force of the coil spring 314 a, 314b, 314 c, 314 d. In this state, since the detection portion 348 a, 348b, 348 c, 348 d of the detection plate 316 a, 316 b, 316 c, 316 d doesnot block the light emitting element 360 a, 360 b, 360 c, 360 d from thelight receiving element 362 a, 362 b, 362 c, 362 d, the overloaddetection sensor 320 a, 320 b, 320 c, 320 d is in the off-state.

From the state shown in FIG. 5 , when an object is placed on the luggagecarrier unit 6 and a load of the luggage carrier unit 6 is applied tothe base plate 20 the pillar member 312 a, 312 b, 312 c, 312 d and thedetection plate 316 a, 316 b, 316 c, 316 d move downward relative to thefront support member 22 (or the rear support member 24) against thebiasing force of the coil spring 314 a, 314 b, 314 c, 314 d. At thisoccasion, when a load that is equal to or than a predetermined upperlimit load (such as 25 kgf) is applied to the pillar member 312 a, 312b, 312 c, 312 d, the detection plate 316 a, 316 b, 316 c, 316 d blocksthe light emitting element 360 a, 360 b, 360 c, 360 d from the lightreceiving element 362 a, 362 b, 362 c, 362 d as shown in FIG. 6 , andthe overload detection sensor 320 a, 320 b, 320 c, 320 d shifts from theoff-state to the on-state. The pillar member 312 a, 312 b, 312 c, 312 dand the detection plate 316 a, 316 b, 316 c, 316 d are configuredcapable of moving downward relative to the base plate 20 until a lowersurface of the circular column 322 a, 322 b, 322 c, 322 d abuts an uppersurface of the base plate 20. By configuring as such, the overloaddetection mechanism 302 is enabled to detect an overload on the luggagecarrier unit 6. For example, in a case where the upper limit load ofeach of the right front overload detection mechanism 302 a, the leftfront overload detection mechanism 302 b, the right rear overloaddetection mechanism 302 c, and the left rear overload detectionmechanism 302 d is 25 kgf, the overload detection mechanism 302 detectsthe overload on the luggage carrier unit 6 when object(s) exceeding 100kg is placed on the luggage carrier unit 6.

As above, the overload detection sensors 320 a, 320 b, 320 c, 320 d arecontactless detection sensors. Due to this, the overload detectionsensors 320 a, 320 b, 320 c, 320 d can be suppressed from being damagedtransmission of vibration or impact applied on the luggage carrier unit6 to the overload detection sensors 320 a, 320 b, 320 c, 320 d.

An overload detection mechanism 364 as shown in FIG. 7 may be used aseach of the right front overload detection mechanism 302 a, the leftfront overload detection mechanism 302 b, the right rear overloaddetection mechanism 302 c, and the left rear overload detectionmechanism 302 d. The overload detection mechanism 364 includes a supportmember 366, a pillar member 368, a coil spring 370, a detection plate372, an upper housing 374, a sensor holder member 376, a lower housing378, an overload detection sensor 380, and a cap 382.

The support member 366 is fixed to the lower surface of the base plate20. The pillar member 368 includes a circular column 384, an uppersmall-diameter portion 386, and a lower small-diameter portion 388. Thecircular column 384 has a substantially circular column shape of whichaxial direction extends along an up-down direction. The uppersmall-diameter portion 386 is arranged above the circular column 384,and has a substantially round columnar shape with a smaller diameterthan the circular column 384. The lower small-diameter portion 388 isarranged below the circular column 384, and has a substantially roundcolumnar shape with a smaller diameter than the circular column 384. Theupper small-diameter portion 385 is inserted from below into a throughhole 390 defined in the support member 366. A threaded hole 392 isdefined at an upper end of the pillar member 368. A bolt 398 is screwfitted in the threaded hole 392 via washers 394, 396. In a state wherethe bolt 398 is screw-fitted in the threaded hole 392, the supportmember 366 is held between the washer 396 and the circular column 384.Since an inner diameter of the through hole 390 is slightly larger thanan outer diameter of the upper small-diameter portion 386, the pillarmember 368 is allowed to slightly fill relative to the support member366.

The lower small-diameter portion 388 and the circular column 384 areinserted from above into a housing chamber 400 defined in the upperhousing 374. The lower small-diameter portion 388 is inserted from aboveinto a through hole 404 defined in a bottom wall 402 of the housingchamber 400. Since an inner diameter of the through hole 404 is slightlylarger than an outer diameter of the lower small-diameter portion 388,the pillar member 368 is allowed to slightly tilt relative to the upperhousing 374. The coil spring 370 is attached to the pillar member 368.An upper end of the coil spring 370 abuts a lower surface of thecircular column 384. A lower end of the coil spring 370 abuts an uppersurface of the bottom wall 402. The coil spring 370 biases the pillarmember 368 upward relative to the upper housing 374. An inner diameterof the housing chamber 400 is slightly larger than an outer diameter ofthe circular column 384. A sealing member 406 configured to slidablyabut a side surface of the circular column 384 is arranged in thevicinity of an upper end of the housing chamber 400. The sealing member406 may for example be a resin O ring. Foreign matters are suppressedfrom entering into the housing chamber 400 by the sealing member 406.Further, a ring-shaped cushion 408 is arranged at an upper end of theupper housing 374.

A threaded hole 410 is defined at a lower end of the pillar member 368.A bolt 412 is screw-fitted in the threaded hole 410 via the detectionplate 372. The detection plate 372 includes a support portion 414 havinga substantially flat plate shape along the front-rear direction and theleft-right direction, and a detection portion 416 that is bent downwardfrom an end of the support portion 414 and having a substantially flatplate shape along the front-rear direction and the up-down direction. Aguide portion 418 for guiding movement of the detection plate 372 in theup-down direction is arranged at a lower portion of the upper housing374.

The sensor holder member 376 is fixed to a lower end of the upperhousing 374. The overload detection sensor 380 is attached to the sensorholder member 370. The overload detection sensor 380 of the presentembodiment is a so-called photo interrupter. The overload detectionsensor 380 includes a light emitting element 420 and a light receivingelement 422 arranged to face each other. The overload detection sensor380 is in an off-state when the light emitting element 420 is notblocked from the light receiving element 422 and is in an on-state whenthe light emitting element 420 is blocked from the light receivingelement 422. The overload detection sensor 380 is electrically connectedto the main control circuit board 44 to be described later (see FIG. 9).

A housing space 424 vertically penetrating the lower housing 378 isdefined in the lower housing 378. A lower portion of the upper housing374 is inserted from above into the housing space 424 of the lowerhousing 378. The detection plate 372, the sensor holder member 376, andthe overload detection sensor 380 are housed in the housing space 424.The lower housing 378 is fixed together with the upper housing 374 tothe front support member 22 (or the rear support member 24). The cap 382is detachably attached to a lower end of the lower housing 378.

As shown in FIG. 7 , in the state where no object is placed on theluggage carrier unit 6 and thus a load from the luggage carrier unit 6is not applied to the base plate 20, an upper surface of the supportportion 414 of the detection plate 372 abuts a lower surface of thebottom wall 402 of the upper housing 374 by a biasing force of the coilspring 370. In this state, since the detection portion 416 of thedetection plate 372 does not block the light emitting element 420 fromthe light receiving element 422, the overload detection sensor 380 is inthe off-state.

From the state shown in FIG. 7 , when an object is placed on the luggagecarrier unit 6 and a load from the luggage carrier unit 6 is applied tothe base plate 20, the pillar member 368 and the detection plate 372move downward relative to the upper housing 374 against the biasingforce of the coil spring 370. At this occasion, when a load that isequal to or greater than the predetermined upper limit load (such as 25kgf) is applied to the pillar member 368, the detection plate 372 blocksthe light emitting element 420 from the light receiving element 422 asshown in FIG. 8 , and the overload detection sensor 380 shifts from theoff-state to the on-state. The pillar member 368 and the detection plate372 are configured capable of moving downward relative to the base plate20 until a lower surface of the support member 366 abuts an uppersurface of the cushion 408. By configuring as such, the overloaddetection mechanism 364 is enabled to detect an overload on the luggagecarrier unit 6.

As above, the overload detection sensor 380 is a contactless detectionsensor. Due to this, the overload detection sensor 380 can be suppressedfrom being damaged by transmission of vibration or impact applied on theluggage carrier unit 6 to the overload detection sensor 380.

In the overload detection mechanism 364, peripheries of the coil spring370, the detection plate 372, and the overload detection sensor 380 aresurrounded by the upper housing 374, the lower housing 378, and the cap382. By configuring as such, foreign matters can be suppressed fromadhering to the coil spring 370, the detection plate 372, and theoverload detection sensor 380 and an operation of the overload detectionmechanism 364 can be suppressed from being adversely affected.

As shown in FIG. 3 , the right upper frame 30 and the left upper frame32 are both members constituted of aluminum, and extend in thefront-rear direction above the base plate 20. The right upper frame 30and the left upper frame 32 are respectively fixed to the upper surfaceof the base plate 20. The upper controller casing 306 is a memberconstituted of resin, and is fixed the upper surface of the base plate20 between the upper frame 30 and the left upper frame 32. As shown inFIG. 9 , an automatic driving control circuit board 426 is housed in theupper controller casing 3306. A wireless interface (hereinbelow may beabbreviated as I/F) 428 (see FIG. 30 ) electrically connected to thereceiver mounted in the carriage unit 4, and an automatic drivingmicro-controller unit (hereinbelow may be termed MCU) 430 (see FIG. 30 )electrically connected to the wireless I/F 428 are mounted on theautomatic driving control circuit board 426. The automatic drivingcontrol circuit board 426 is electrically connected to the main controlcircuit board 44 to be described later.

As shown in FIG. 3 , the battery box 34 is a member constituted ofresin, and is arranged below the base plate 20 in the vicinity of therear portion of the base plate 20. The battery box 34 is fixed to therear support member 24. As shown in FIG. 9 , a battery receptacle 40 towhich a battery pack 38 can detachably be attached is arranged insidethe battery box 34. The battery pack 38 includes secondary battery cellssuch as lithium ion battery cells. The cart 2 is configured to operateby power supplied from the battery pack 38 attached to the batteryreceptacle 40. An openable battery cover 42 is arranged at a rearportion of the battery box 34. The battery pack 38 can be attached to ordetached from the battery receptacle 40 by sliding the battery pack 38in the front-rear direction relative to the battery receptacle 40 in astate of having the battery cover 42 opened.

As shown in FIG. 2 , the lower controller casing 36 is a memberconstituted of resin, and is arranged below the base plate 20 in thevicinity of a center of the base plate 20. The lower controller casing36 is fixed to the right lower frame 26 and the left lower frame 28 in astate of being placed on an upper surface of the right lower frame 26and an upper surface of left lower frame 28. As Shown in FIGS. 9 and 10, the lower controller casing 36 holds one main control circuit board44, two drive control circuit boards 46, 48, and four electrical brakecircuit boards 50, 52, 54, 56.

As shown in FIG. 9 , the main control circuit board 44 is housed in acircuit board casing 44 a. The circuit board casing 44 a is housed on aback side within the lower controller casing 36. The circuit boardeasing 44 a is arranged such that the main control circuit board 44 isarranged along the up-down direction and the left-right direction. Acontrol power supply circuit 432, a main MCU 434, a switch circuit 436,shutoff circuits 438, 440, 442 (see FIG. 30 ) to be described later aremounted on the main control circuit board 44.

As shown in FIG. 10 , the drive control circuit boards 46, 48 arerespectively housed inside circuit board casings 46 a, 48 a. As shown inFIG. 9 , the circuit board casings 46 a, 48 a are housed on a frontlower side within the lower controller casing 36. The circuit boardcasings 46 a, 48 a are respectively arranged such that the drive controlcircuit boards 46, 48 are arranged along the front-rear direction andthe left-right direction. The drive control circuit boards 46, 48 areelectrically connected to the main control circuit board 44. Motor MCUs444, 448, 452, motor drivers 454, 458, 462 and an electromagnetic brakedriver 464 (see FIG. 30 ) to be described later are mounted on the drivecontrol circuit board 46. Motor MCUs 446, 450, 452, motor drivers 456,460, and an electromagnetic brake driver 466 (see FIG. 30 ) to bedescribed later are mounted on the drive control circuit board 48.

As shown in FIG. 10 , the electrical brake circuit boards 50, 52, 54, 56are respectively attached to heat dissipating casings 50 a, 52 a, 54 a,56 a. The heat dissipating casings 50 a, 52 a, 54 a, 56 a respectivelyinclude circuit board housings 50 b, 52 b, 54 b, 56 b housing theelectrical brake circuit boards 50, 52, 54, 56, heat dissipating fins 50c, 52 c, 54 c, 56 c, and cooling fans 50 d, 52 d, 54 d, 56 d. The heatdissipating casings 50 a, 52 a are housed at a front upper side withinthe lower controller casing 36. The heat dissipating casings 50 a, 52 aare arranged such that the electrical brake circuit boards 50, 52 arearranged along the front-rear direction and the left-right direction andthe cooling fans 50 d, 52 d are oriented upward. The heat dissipatingcasings 54 a, 56 a are fixed to a heat dissipating plate 58 fixed to thelower controller casing 36 on an outer side thereof at a front lowerportion of the lower controller casing 36. The heat dissipating casings54 a, 56 a are arranged such that the electrical brake circuit boards54, 56 are arranged along the front-rear direction and the left-rightdirection and the cooling fans 54 d, 56 d are oriented downward. Theelectrical brake circuit boards 50, 54 and the cooling fans 50 d, 54 dare electrically connected to the drive control circuit board 46. Theelectrical brake circuit boards 52, 56 and the cooling fans 52 d, 56 dare electrically connected to the drive control circuit board 48. Brakecircuits 468, 470, 472, 474 (see FIG. 30 ) to be described later aremounted respectively on the electrical brake circuit boards 50, 52, 54,56.

(Platform Unit 6)

As shown in FIG. 1 , the luggage carrier unit 6 includes a main frame60, a right guard 62, a left guard 64, and a front guard 66. The mainframe 60, the right guard 62, the left guard 64, and the front guard 66are respectively constituted of steel round pipes. The main frame 60 isarranged above the base plate 20 of the carriage unit 4 and along thefront-rear direction and the left-right direction. The main frame 60 isfixed to the right upper frame 30 and the left upper frame 32 in a stateof being placed on upper surfaces of the right upper frame 30 and theleft upper frame 32 of the carriage unit 4. An object to be carried bythe cart 2 is to be placed on an upper surface of the main frame 60. Theright guard 62 is attached to a right end of the main frame 60 so as toprotrude higher than the upper surface of the main frame 60. The rightguard 62 is arranged along the front-rear direction and the up-downdirection. The left guard 64 is attached to a left end of the main frame60 so as to protrude higher than the upper surface of the main frame 60.The left guard 64 is arranged along the front-rear direction and theup-down direction. The front guard 66 is attached to a front end of themain frame 60 so as to protrude higher than the upper surface of themain frame 60. The front guard 66 is arranged along the left-rightdirection and the up-down direction.

(Handle Unit 8)

As shown in FIG. 11 , the handle unit 8 includes a switch box 70, aright handle 72, a left handle 74, a handle arm 76, a support pipe 78, aclamping member 80, a fixing member 82, a handle shaft 84, a base member86, a rotation angle sensor 88, a movable cam member 90, a fixed cammember 92, and a coil spring 94. Hereinbelow, the right handle 72, theleft handle 74, the handle arm 76, and the support pipe 78 maycollectively be termed a steering handle 73.

The switch box 70 includes a main power switch 96, a mode shifter switch98, a trigger switch 100, a travelling direction shifter switch 102, aspeed shifter switch 104, a horn switch 106, and LEDs 476. The mainpower switch 96 is configured to switch main power of the cart 2 betweenon and off. The mode shifter switch 98 is configured to switch anoperation mode of the cart 2 between the manual mode, the automaticmode, and the parking mode. The trigger switch 100 is configured toswitch on/off of a forward motion and a backward motion of the cart 2 inthe manual mode, and to adjust a travelling speed of the cart 2. Thetravelling direction shifter switch 102 is configured to switch atravelling direction of the cart 2 in the manual mode. The speed shifterswitch 104 is configured to switch an upper limit travelling speed ofthe cart 2 in the manual mode. The horn switch 106 is configured tosound a horn using a buzzer 478 (see FIG. 30 ) incorporated in theswitch box 70. The LEDs 476 are configured to display on/off of the mainpower of the cart 2, and also the travelling direction and the upperlimit travelling speed that are currently set. The main power switch 96,the mode shifter switch 98, the trigger switch 100, the travellingdirection shifter switch 102, the speed shifter switch 104, the hornswitch 106, the LEDs 476, and the buzzer 478 are respectivelyelectrically connected to the main control circuit board 44 (see FIG. 9).

The right handle 72 comprises a support portion 72 a extending in theup-down direction and a handle portion 72 b that is bent rightward froman upper end of the support portion 72 a. A lower end of the supportportion 72 a is fixed to the handle arm 76. A right grip 72 c isarranged at a right end of the handle portion 72 b. The switch box 70 isfixed to the handle portion 72 b on the left side of the right grip 72c. The left handle 74 comprises a support portion 74 a extending in theup-down direction and a handle portion 74 b that is bent leftward froman upper end of the support portion 74 a. A lower end of the supportportion 74 a is fixed to the handle arm 76. A left grip 74 c is arrangedat a left end of the handle portion 74 b. An upper end of the supportpipe 78 is fixed to the handle arm 76. The support pipe 78 extends inthe up-down direction. The clamping member 80 includes clamping parts 80a, 80 b configured to clamp the support pipe 78 from both left and rightsides. A tightening part 80 c that is tightened by a tightening tool(not shown) is arranged at rear ends of the clamping parts 80 a, 80 b.When the tightening tool of the tightening part 80 c is tightened, tireclamping parts 80 a, 80 b are firmly pressed against an outer surface ofthe support pipe 78, and the support pipe 78 is thereby fixed relativeto the clamping member 80. When the tightening tool of the tighteningpart 80 c is loosened, the clamping parts 80 a, 80 b are no longerpressed against the outer surface of the support pipe 78, and thesupport pipe 78 thereby becomes movable in the up-down directionrelative to the clamping member 80, and also pivotable about the up-downdirection. A position and an angle of the support pipe 78 relative tothe clamping member 80 can be fixed by adjusting the support pipe 78 toa desired position and angle relative to the clamping member 80 in astate of having the tightening tool of the tightening part 80 cloosened, and thereafter tightening the tightening tool of thelightening part 80 c.

As shown in FIG. 12 , a front portion of the clamping member 80 is fixedto the fixing member 82. An upper end of the handle shaft 84 is fixed tothe fixing member 82. A lower end of the handle shaft 84 is pivotablysupported by the base member 86. The base member 86 is fixed to theupper surface of the base plate 20 of the carriage unit 4. The rotationangle sensor 88 is fixed under the base member 86. The rotation anglesensor 88 is coupled to the lower end of the handle shaft 84. Therotation angle sensor 88 is configured to detect a rotation angle of thehandle shaft 84 relative to the base member 86. The rotation anglesensor 88 may for example be a potentiometer configured to detect achange in an electric resistance value that is obtained in accordancewith a change in a rotation angle. Alternatively, the rotation anglesensor 88 may be a magnetic rotary sensor including a Hall element ofwhich position is fixed relative to the base member 86 and a permanentmagnet of which position is fixed relative to the handle shaft 84. Therotation angle sensor 88 is electrically connected to the main controlcircuit board 44 (see FIG. 9 ).

As shown in FIG. 13 , the handle shaft 84 includes a guiding protrusion84 a. The guiding protrusion 84 a extends radially outward from an outercircumferential surface of the handle shaft 84, and extends along anaxial direction of the handle shaft 84.

As shown in FIG. 14 , the movable cam member 90 has a substantiallycylindrical shape. Cam projections 90 a, 90 b extending downward arearranged at a lower portion of the movable cam member 90. The camprojections 90 a, 90 b respectively include a first cam surface 90 c, 90d and a second cam surface 90 e, 90 f. The first cam surface 90 c, 90 dis inclined downward at an increasing degree in a clockwise direction ina top view of the movable cam member 90. The second cam surface 90 e, 90f is inclined upward at an increasing degree in a counterclockwisedirection in the top view of the movable cam member 90. A guiding groove90 g is defined on an inner circumferential surface of the movable cammember 90. The guiding groove 90 g has a width corresponding to theguiding protrusion 84 a (see FIG. 13 ), and extends in a directionparallel to a center axis of the movable cam member 90. When the movablecam member 90 is to be attached to the handle shaft 84, the guidingprotrusion 84 a engages with the guiding groove 90 g in a state of beingslidable in the up-down direction. Due to this, the movable cam member90 is held by the handle shaft 84 so as to be movable in the up-downdirection. A spring receiving portion 90 h configured to support thecoil spring 94 is arranged at an upper portion of the movable cam member90. As shown in FIG. 12 , the coil spring 94 is configured to bias themovable cam member 90 downward relative to the fixing member 82.

As shown in FIG. 15 , the fixed cam member 92 includes a cylinderportion 92 a having a substantially cylindrical shape and a flange 92 bextending radially outward from a lower end of the cylinder portion 92a. The fixed cam member 92 is fixed to the base member 86 by having theflange 92 b fastened on an upper surface of the base member 86 (see FIG.12 ) by a fastening member (not shown). Cam recesses 92 c, 92 dcorresponding to the cam projections 90 a, 90 b of the movable cammember 90 are defined at an upper portion of the cylinder portion 92 a.The cam recesses 92 c, 92 d respectively have a first cam surface 92 e,92 f and a second cam surface 92 g, 92 h. The first cam surface 92 e, 92f corresponds to its corresponding first cam surface 90 c, 90 d of themovable cam member 90. The second cam surface 92 g, 92 h corresponds toits corresponding second cam surface 90 e, 90 f of the movable cammember 90. Further, stopper portions 92 i, 92 j are arranged on an innercircumferential surface of the cylinder portion 92 a. As shown in FIG.16 , the stopper portions 92 i, 92 j are configured to restrict arotatable pivotable range of the handle shaft 84 by coming into abutmentwith the guiding protrusion 84 a of the handle shaft 84 when the handleshaft 84 pivots relative to the fixed cam member 92.

In the handle unit 8 shown in FIG. 11 , when the user rotates thesteering handle 73 in a clockwise (or counterclockwise) direction asseen from above, the handle shaft 84 pivots in the clockwise (orcounterclockwise) direction. At this occasion, as shown in FIG. 17 , dueto the movable cam member 90 pivoting integrally with the handle shaft84, the first cam surface 90 c, 90 d (or the second cam surface 90 e, 90f) of the movable cam member 90 slides relative to the first cam surface92 e, 92 f (or the second cam surface 92 g, 92 h) of the fixed cammember 92, as a result of which the movable cam member 90 moves upwardagainst the biasing force of the coil spring 94 as it pivots relative tothe fixed cam member 92. In operating as such, torque generated by areaction force which the movable cam member 90 receives from the fixedcam member 92 acts on the user rotating the steering handle 73.

(Steering Unit 10)

As shown in FIG. 18 , the steering unit 10 is attached to the frontsupport member 22 below the front portion of the base plate 20 of thecarriage unit (see FIG. 2 ). The steering unit 10 is linked to the frontwheel unit 12, and is configured to steer the front wheel unit 12.

As shown in FIG. 19 , the steering unit 10 includes a motor housing 160,a motor support member 162, a gear housing 164, a steering angle sensor166, a steering shaft 168, a steering plate 170, a right tie rod 172,and a left tie rod 174. The motor housing 160 is fixed to the motorsupport member 162. The motor support member 162 is fixed to the gearhousing 164. The gear housing 164 is fixed to the front support member22 of the carriage unit 4 (see FIG. 18 ).

As shown in FIG. 20 , a steering motor 176 is housed inside the motorhousing 160. The steering motor 176 may for example be an inner rotorbrushless DC motor. The steering motor 176 is electrically connected tothe drive control circuit board 46 (see FIG. 10 ). The steering motor176 includes a motor shaft 176 a extending in the front-rear directionand a Hall sensor 480 (see FIG. 34 ) configured to detect rotation ofthe motor shaft 176 a. The motor shaft 176 a is rotatably held by themotor housing 160 in the vicinity of its rear end and is rotatably heldby the motor support member 162 at its front portion. The front portionof the motor shaft 176 a penetrates through the motor support member 162and enters into the gear housing 164. A gear portion 176 b is arrangedin the vicinity of a front end of the motor shaft 176 a.

A spindle 178, a cam wheel 180, a movable gear 182, a coil spring 184, acylindrical worm 186, a worm wheel 188, and a relay shaft 190 are housedin the gear housing 164. The spindle 178 is arranged along thefront-rear direction. The spindle 178 is rotatably held by the gearhousing 164 in the vicinity of its front end and its rear portion.Further, the spindle 178 is rotatably held by the motor support member162 in the vicinity of its rear end.

The cam wheel 180 is fixed to the vicinity of the rear end of thespindle 178. As shown in FIG. 21 , cam grooves 180 a are defined in afront surface of the cam wheel 180. The movable gear 182 is attached tothe spindle 178 at a position frontward from the cam wheel 180. Themovable gear 182 is held by the spindle 178 so as to be configuredcapable of moving in the front-rear direction relative to the spindle178 and capable of rotating about the front-rear direction. A gear unit182 a configured to mesh with the gear portion 176 b of the motor shaft176 a is arranged on an outer circumferential surface of the movablegear 182 (see FIG. 20 ). A recess 182 b into which the cam wheel 180 isto enter is defined in a rear portion of the movable gear 182. Camprojections 182 c corresponding to the cam grooves 180 a of the camwheel 180 are arranged in the recess 182 b. The coil spring 184 isattached to the spindle 178 at a position frontward from the movablegear 182. The coil spring 184 is held by a spring receiving portion 178a arranged on the spindle 178. The coil spring 184 is configured to biasthe movable gear 182 backward relative to the spindle 178.

When the motor shaft 176 a (see FIG. 20 ) rotates, the movable gear 182also rotates. In a case where the cam projections 182 c of the movablegear 182 are engaged with the cam grooves 180 a of the cam wheel 180,the cam wheel 180 rotates accompanying rotation of the movable gear 182,as a result of which the spindle 178 also rotates. When torque actingbetween the movable gear 182 and the cam wheel 180 is small, engagementof the cam projections 182 c and the cam grooves 180 a is maintained bya biasing force of the coil spring 184, and transmission of the rotationfrom the motor shaft 176 a to the spindle 178 is maintained. Contrary tothis, when the torque acting between the movable gear 182 and the camwheel 180 is large, the movable gear 182 moves forward against thebiasing force of the coil spring 184, by which the engagement of the camprojections 182 c and the cam grooves 180 a is released, and thetransmission of the rotation from the motor shaft 176 a to the spindle178 is thereby blocked. That is, a torque limiter 181 is constituted bythe cam wheel 180, the movable gear 182, and the coil spring 184.

As shown in FIG. 20 , the cylindrical worm 186 is fixed to a frontportion of the spindle 178. T be worm wheel 188 is arranged to mesh withthe cylindrical worm 186. As shown in FIG. 22 , the worm wheel 188 isfixed to an upper portion of the relay shaft 190. The relay shaft 190 isarranged along the up-down direction. The relay shaft 190 is rotatablyheld by the gear housing 164 in the vicinity of its upper end and at itscenter portion. A gear unit 190 a is arranged in the vicinity of a lowerend of the relay shaft 190.

The steering angle sensor 166 is fixed to an upper portion of the gearhousing 164. The steering angle sensor 166 is coupled to the upper endof the relay shaft 190. The steering angle sensor 166 is configured todetect a rotation angle of the relay shaft 190 relative to the gearhousing 164. The steering angle sensor 166 may for example be apotentiometer configured to detect a change in an electric resistancethat occurs in accordance with a change in the rotation angle.Alternatively, the steering angle sensor 166 may be a magnetic rotarysensor having a Hall element of which position is fixed relative to thegear housing 164 and a permanent magnet of which position is fixedrelative to the relay shaft 190. The steering angle sensor 166 iselectrically connected to the main control circuit hoard 44 (see FIG. 9).

The steering shaft 168 is rotatably held by the gear housing 164 in thevicinity of its upper end and at its upper portion. The steering shaft168 is arranged along the up-down direction. A gear unit 168 aconfigured to mesh with the gear unit 190 a of the relay shaft 190 isarranged at the upper portion of the steering shaft 168. A lower end ofthe steering shaft 168 is fixed to the vicinity of a front end of thesteering plate 170. As shown in FIG. 19 , the steering plate 170 has anarrow flat plate shape having its longitudinal direction along thefront-rear direction and its short direction along the left-rightdirection. A rear end of the right tie rod 172 and a rear end of theleft tie rod 174 are respectively coupled in the vicinity of a rear endof the steering plate 170. The rear end of the right tie rod 172 iscoupled to the steering plate 170 so as to be pivotable about two axesorthogonal to the longitudinal direction of the right tie rod 172. Therear end of the left tie rod 174 is coupled to the steering plate 170 soas to be pivotable about two axes orthogonal to the longitudinaldirection of the left tie rod 174.

As shown in FIG. 20 , when the spindle 178 rotates by the rotation ofthe motor shaft 176 a, the rotation of the spindle 178 is transmitted tothe relay shaft 190 through the cylindrical worm 186 and the worm wheel188. As shown in FIG. 22 , when the relay shaft 190 pivots, the steeringshaft 168 pivots accordingly, and the rear end of the steering plate 170pivots in the left-right direction. Due to the steering plate 170pivoting as above, the right tie rod 172 and the left tie rod 174 asshown in FIG. 19 move, and steering of the front wheel unit 12 isthereby performed. In the following description, the steering shaft 168,the steering plate 170, the right tie rod 172, the left tie rod 174, thespindle 178, the torque limiter 181, the cylindrical worm 186, the wormwheel 188, and the relay shaft 190 may collectively be termed atransmission mechanism 169.

In the manual mode, the main control circuit board 44 (see FIG. 9 )calculates a steering angle that should be realized in the steering unit10 based on a detection signal from the rotation angle sensor 88 of thehandle unit 8 (see FIG. 11 ). Then, the main control circuit board 44calculates a rotation angle that should be realized in the steeringmotor 176 based on the steering angle that should be realized in thesteering unit 10, and instructs the drive control circuit board 46 toacuate the steering motor 176. Due to this, the steering angleresponsive to the user operation on the handle unit 8 is realized in thesteering unit 10.

(Front Wheel Unit 12)

As shown in FIG. 18 , the front wheel unit 12 is attached to the frontsupport member 22 below the front portion of the base plate 20 of thecarriage unit 4 (see FIG. 2 ). The front wheel unit 12 includes a rightfront wheel unit 12 a and a left front wheel unit 12 b. The right frontwheel unit 12 a includes a right front wheel 192, a right gear housing194, a right motor housing 196, a right kingpin 198, a right sleeve 200,a right upper arm 202, a right lower arm 204, a right buffer member 206,and a right steering plate 208. The left front wheel unit 12 b includesa left front wheel 212, a left gear housing 214, a left motor housing216, a left kingpin 218, a left sleeve 220, a left upper arm 222, a leftlower arm 224, a left buffer member 226, and a left steering plate 228.In the following description, the right gear housing 194, the rightkingpin 198, the right sleeve 200, and the right steering plate 208 maycollectively be termed a right holding member 195, and the left gearhousing 214, the left kingpin 218, the left sleeve 220, and the leftsteering plate 228 may collectively be termed a left holding member 215.Further, the right holding member 195, the right upper arm 202, theright lower arm 204, the right buffer member 206, the left holdingmember 215, the left upper arm 222, the left lower arm 224, the leftbuffer member 226, and the steering unit 10 may collectively be termed asuspension mechanism 11.

As shown in FIG. 23 , the right gear housing 194 is arranged to the leftof the right front wheel 192. The right motor housing 196 is fixed to aleft portion of the right gear housing 194. As shown in FIG. 24 , aright front wheel motor 232 is housed inside the right motor housing196. The right front wheel motor 232 may for example be an inner rotorbrushless DC motor. The right front wheel motor 232 is electricallyconnected to the drive control circuit board 46 (see FIG. 10 ). Theright front wheel motor 232 includes a right front wheel motor shaft 232a extending in the left-right direction and a Hall sensor 482 configuredto detect rotation of the right front wheel motor shaft 232 a (see FIG.32 ). The right front wheel motor shaft 232 a is rotatably held by theright motor housing 196 in the vicinity of its left end, and isrotatably held by the right gear housing 194 in the vicinity of itsright end. The right front wheel 192 includes a right front wheel axle192 a extending leftward. The right front wheel axle 192 a is rotatablyheld by the right gear housing 194 in the vicinity of its left end. Aplanetary gear mechanism 234 is housed inside the right gear housing194. The planetary gear mechanism 234 is configured to decelerate therotation of the right front wheel motor shaft 232 a and transmit thesame to the right front wheel axle 192 a. When the right front wheelmotor 232 is driven, the rotation of the right front wheel motor shaft232 a is transmitted to the right front wheel axle 192 a through theplanetary gear mechanism 234, as a result of which the right front wheel192 rotates.

The right kingpin 198 is fixed to an upper portion of the right gearhousing 194. The right kingpin 198 extends along the up-down direction.An upper portion of the right kingpin 198 enters inside the right sleeve200. The right kingpin 198 is rotatably held by the right sleeve 200 invicinities of upper and lower ends of the right sleeve 200. As shown inFIG. 23 , a right end of the right upper arm 202 is coupled to an upperportion of the right sleeve 200 so as to be pivotable about a pivot axisalong the front-rear direction A, right end of the right lower arm 204is coupled to a lower portion of the right sleeve 200 so as to bepivotable about a pivot axis along the front-rear direction. As shown inFIG. 18 , a left end of the right upper arm 202 is coupled to a rightupper coupling portion 22 a of the front support member 22 so as to bepivotable about a pivot axis along the front-rear direction. A left endof the right lower arm 204 is coupled to a right lower coupling portion22 b of the front support member 22 so as to be pivotable about a pivotaxis along the front-rear direction. Due to this, the right sleeve 200is supported by the front support member 22 so as to be movable within amovable range of the right upper arm 202 and the right lower arm 204.

The right buffer member 206 includes a damper 206 a and a coil spring206 b. An upper end of the right buffer member 206 is coupled to a frontsurface of the front support member 22 so as to be pivotable about apivot axis along the front-rear direction. A lower end of the rightbuffer member 206 is coupled to a front surface of the right lower arm204 so as to be pivotable about a pivot axis along the front-reardirection. Due to this, when the right front wheel 192 moves in theup-down direction relative to the front support member 22, impacts andvibration from the right front wheel 192 are suppressed from beingtransmitted to the carriage unit 4 by a damping force of the damper 206a and an elastic restoration force of the coil spring 206 b.

As shown in FIG. 23 , the right steering plate 208 is fixed to thevicinity of a lower end of the right kingpin 198. A front end of theright tie rod 172 is coupled to a left front end of the right steeringplate 208 so as to be pivotable about two axes orthogonal to thelongitudinal direction of the right tie rod 172. When the right frontwheel unit 12 a is seen from above, the right tie rod 172 intersectswith the right upper arm 202 and the right lower arm 204. When the frontwheel unit 12 is steered to the right (or left), a rear end of thesteering plate 170 (see FIG. 19 ) moves rightward (or leftward), bywhich the right steering plate 208, the right kingpin 198, the rightgear housing 194, the right motor housing 196, and the right front wheel192 pivot clockwise (or counterclockwise) relative to the right sleeve200 with an axial direction of the right kingpin 198 as their pivotingaxes in a top view seeing the right sleeve 200 from above.

As shown in FIG. 18 , the left front wheel unit 12 b has a configurationthat is in a left-right symmetric relationship with the right frontwheel unit 12 a. Hereinbelow, the left front wheel unit 12 b will bedescribed with reference to FIGS. 23 and 24 showing the right frontwheel unit 12 a.

As shown in FIG. 23 , the left gear housing 214 is arranged to the rightof the left front wheel 212. The left motor housing 216 is fixed to aright portion of the left gear housing 214. As shown in FIG. 24 , a leftfront wheel motor 242 is housed inside the left motor housing 216. Theleft front wheel motor 242 may for example be an inner rotor brushlessDC motor. The left front wheel motor 242 is electrically connected tothe drive control circuit board 48 (see FIG. 10 ). The left front wheelmotor 242 includes a left front wheel motor shaft 242 a extending in theleft-right direction and a Hall sensor 484 configured to detect rotationof the left front wheel motor shaft 242 a (see FIG. 32 ). The left frontwheel motor shaft 242 a is rotatably held by the left motor housing 216in the vicinity of its right end, and is rotatably held by the left gearhousing 214 in the vicinity of its left end. The left front wheel 212includes a left axle 212 a extending rightward. The left axle 212 a isrotatably held by the left gear housing 214 in the vicinity of its rightend. A planetary near mechanism 244 is housed inside the left gearhousing 214. The planetary gear mechanism 244 is configured todecelerate the rotation of the left front wheel motor shaft 242 a andtransmit the same to the left axle 212 a. When the left front wheelmotor 242 is driven, the rotation of the left front wheel motor shaft242 a is transmitted to the left axle 212 a through the planetary gearmechanism 244, as a result of which the left front wheel 212 rotates.

The left kingpin 218 is fixed to an upper portion of the left gearhousing 214. The left kingpin 218 extends along the up-down direction.An upper portion of the left kingpin 218 enters inside the left sleeve220. The left kingpin 218 is rotatably held by the left sleeve 220 invicinities of upper and lower ends of the left sleeve 220. As shown inFIG. 23 , a left end of the left upper arm 222 is coupled to an upperportion of the left sleeve 220 so as to be pivotable about a pivot axisalong the front-rear direction. A left end of the left lower arm 224 iscoupled to a lower portion of the left sleeve 220 so as to be pivotableabout a pivot axis along the front-rear direction. As shown in FIG. 18 ,a right end of the left upper arm 222 is coupled to a left uppercoupling portion 22 c of the front support member 22 so as to bepivotable about a pivot axis along the front-rear direction. A right endof the left lower arm 224 is coupled to a left lower coupling portion 22d of the front support member 22 so as to be pivotable about a pivotaxis along the front-rear direction. Due to this, the left sleeve 220 issupported by the front support member 22 so as to be movable within amovable range of the left upper arm 222 and the left lower arm 224.

The left buffer member 226 includes a damper 226 a and a coil spring 226b. An upper end of the left buffer member 226 is coupled to the frontsurface of the front support member 22 so as to be pivotable about apivot axis along the front-rear direction. A lower end of the leftbuffer member 226 is coupled to the front surface of the left lower arm224 so as to be pivotable about a pivot axis along the front-reardirection. Due to this, when the left front wheel 212 moves in theup-down direction relative to the front support member 22, impacts andvibration from the left front wheel 212 are suppressed from beingtransmitted to the carriage unit 4 by a damping force of the damper 226a and an elastic restoration force of the coil spring 226 b.

As shown in FIG. 23 , the left steering plate 228 is fixed to thevicinity of a lower end of the left kingpin 218. A front end of the lefttie rod 174 is coupled to a right front end of the left steering plate228 so as to be pivotable about two axes orthogonal to the longitudinaldirection of the left tie rod 174. When the left front wheel unit 12 bis seen from above, the left tie rod 174 intersects with the left upperarm 222 and the left lower arm 224. When the front wheel unit 12 issteered to the right (or left), a rear end of the steering plate 170(see FIG. 19 ) moves rightward (or leftward), by which the left steeringplate 228, the left kingpin 218, the left gear housing 214, the leftmotor housing 216, and the left front wheel 212 pivot clockwise (orcounterclockwise) relative to the left sleeve 220 with an axialdirection of the left kingpin 218 as their pivoting axes in a top viewseeing the left Sleeve 220 from above.

(Rear Wheel Unit 14)

As shown in FIG. 25 , the rear wheel unit 14 is attached to the rearsupport member 24 below a rear portion of the base plate 20 of thecarriage unit 4 (see FIG. 2 ). The rear wheel unit 14 includes a rightrear wheel unit 14 a and a left rear wheel unit 14 b. The right rearwheel unit 14 a includes a right rear wheel 252, a right gear housing254, a right motor housing 256, a right brake housing 258, a rightclutch lever 260, and a right buffer member 264. The left rear wheelunit 14 b include a left rear wheel 272, a left gear housing 274, a leftmotor housing 276, a left brake housing 278, a left clutch lever 280,and a left buffer member 284.

As shown in FIG. 26 , the right gear housing 254 is arranged to the leftof the right rear wheel 252 and rotatably holds a right rear wheel axle(not shown) of the right rear wheel 252, The right gear housing 254extends upward toward the front from the right rear wheel axle. Theright motor housing 256 is fixed to the left of a front upper portion ofthe right gear housing 254. The right brake housing 258 is fixed to theleft of the right motor housing 256. A right rear Wheel motor 486 (seeFIG. 30 ) is housed in the right motor housing 256. The right rear wheelmotor 486 may for example be an inner rotor brushless DC motor. Theright rear wheel motor 486 is electrically connected to the drivecontrol circuit board 46 (see FIG. 10 ). The right rear wheel motor 486includes a right rear wheel motor shaft (not shown) extending in theleft-right direction and a Hall sensor 488 configured to detect rotationof the right rear wheel motor shaft (see FIG. 32 ). A right rear wheelelectromagnetic brake 490 (see FIG. 30 ) is housed in the right brakehousing 258. The right rear wheel electromagnetic brake 490 is coupledto the right rear wheel motor shaft. The right rear wheelelectromagnetic brake 490 is configured to switch between a stateallowing the right rear wheel motor shaft to rotate and a stateprohibiting the same from rotating. The right rear wheel electromagneticbrake 490 is electrically connected to the drive control circuit board46 (see FIG. 10 ). In the parking mode, the right rear wheelelectromagnetic brake 490 is maintained in the state prohibiting theright rear wheel motor shaft from rotating.

A spur gear mechanism (not shown) and a clutch mechanism (not shown) arehoused in the right gear housing 254. The spur gear mechanism isconfigured to decelerate the rotation of the right rear wheel motorshaft and transmits the same to the right rear wheel axle. When theright rear wheel motor 486 is driven, the rotation of the right rearwheel motor shaft is transmitted to the right rear Wheel axle throughthe spur gear mechanism, and the right rear wheel 252 thereby rotates.The clutch mechanism is configured to switch between a state allowingtransmission of the rotation from the right rear wheel motor shaft tothe right rear wheel axle and a state prohibiting to do so in responseto an operation performed on the right clutch lever 260. Due to this, byswitching the clutch mechanism to the state prohibiting the transmissionof the rotation from the right rear wheel motor shaft to the right rearwheel axle when the right rear wheel electromagnetic brake 490 prohibitsthe rotation of the right rear wheel motor shaft, the right rear wheel252 can be suppressed from being locked.

A coupling portion 254 a is arranged in the vicinity of a front upperend of the right gear housing 254. The coupling portion 254 a is coupledto the rear support member 24 so as to be pivotable about a pivot axisalong the left-right direction. The right buffer member 264 includes adamper 264 a and a coil spring 264 b. An upper end of the right buffermember 264 is coupled to the rear support member 24 at a rear upperportion from the coupling portion 254 a so as to be pivotable about apivot axis along the left-right direction. A lower end of the rightbuffer member 264 is coupled to a rear upper surface of the right gearhousing 254 so as to be pivotable about a pivot axis along theleft-right direction. Due to this, when the right rear wheel 252 movesin the up-down direction relative to the rear support member 24, impactsand vibration from the right rear wheel 252 are suppressed from beingtransmitted to the carriage unit 4 by a damping force of the damper 264a and an elastic restoration force of the coil spring 264 b.

As shown in FIG. 25 , the left rear wheel unit 14 b has a configurationthat is in a left-right symmetric relationship with the right rear wheelunit 14 a. Hereinbelow, the left rear wheel unit 14 b will be describedwith reference to FIG. 26 showing the right rear wheel unit 14 a.

As shown in FIG. 26 , the left gear housing 274 is arranged to the rightof the left rear wheel 272 and rotatably holds a left rear wheel axle(not shown) of the left rear wheel 272. The left gear housing 274extends upward toward the front from the left rear wheel axle. The leftmotor housing 276 is fixed to the right of a front upper portion of theleft gear housing 274. The left brake housing 278 is fixed to the rightof the left motor housing 276, left rear wheel motor 492 (see FIG. 30 )is housed in the left motor housing 276. The left rear wheel motor 492may for example be an inner rotor brushless DC motor. The left rearwheel motor 492 is electrically connected to the drive control circuitboard 48 (see FIG. 10 ). The left rear wheel motor 492 includes a leftrear wheel motor shaft (not shown) extending in the left-right directionand a Hall sensor 494 configured to detect rotation of the left rearwheel motor shaft (see FIG. 32 ). A left rear wheel electromagneticbrake 496 (see FIG. 30 ) is housed in the left brake housing 278. Theleft rear wheel electromagnetic brake 496 is coupled to the left rearwheel motor shaft. The left rear wheel electromagnetic brake 496 isconfigured to switch between a state allowing the left rear wheel motorshaft to rotate and a state prohibiting the same from rotating. The leftrear wheel electromagnetic brake 496 is electrically connected to thedrive control circuit board 48 (see FIG. 10 ). The drive control circuitboard 48 is configured to control operations of the left rear wheelelectromagnetic brake 496. In the parking mode, the left rear wheelelectromagnetic brake 496 is maintained in the state prohibiting theleft rear wheel motor shaft from rotating.

A spur gear mechanism (not shown) and a clutch mechanism (not shown) arehoused in the left gear housing 274. The spur gear mechanism isconfigured to decelerate the rotation of the left rear wheel motor shaftand transmit the same to the left rear wheel axle. When the left rearwheel motor 492 is driven, the rotation of the left rear wheel motorshaft is transmitted to the left rear wheel axle through the spur gearmechanism, and the left rear wheel 272 thereby rotates. The clutchmechanism is configured to switch between a state allowing transmissionof the rotation from the left rear wheel motor shaft to the left rearwheel axle and a state prohibiting to do so in response to an operationperformed on the left clutch lever 280. Due to this, by switching theclutch mechanism to the state prohibiting the transmission of therotation from the left rear wheel motor shaft to the left rear wheelaxle when the left rear wheel electromagnetic brake 496 prohibits therotation of the left rear wheel motor shaft, the left rear wheel 272 canbe suppressed from being locked.

A coupling portion 274 a is arranged in the vicinity of a front upperend of the left gear housing 274. The coupling portion 274 a is coupledto the rear support member 24 so as to be pivotable about a pivot axisalong the left-right direction. The left buffer member 284 includes adamper 284 a and a coil spring 284 b. An upper end of the left buffermember 284 is coupled to the rear support member 24 at a rear upperportion from the coupling portion 274 a so as to be pivotable about apivot axis along the left-right direction. A lower end of the leftbuffer member 284 is coupled to a rear upper surface of the left gearhousing 274 so as to be pivotable about a pivot axis along theleft-right direction. Due to this, when the left rear wheel 272 moves inthe up-down direction relative to the rear support member 24, impactsand vibration from the left rear wheel 272 are suppressed from beingtransmitted to the carriage unit 4 by a damping force of the damper 284a and an elastic restoration force of the coil spring 284 b.

(Bumper Unit 16)

As shown in FIG. 1 , the bumper unit 16 is attached to the front supportmember 22 below the front portion of the base plate 20 of the carriageunit 4. As shown in FIG. 27 , the bumper unit 16 includes a base member500, a housing 502, a right front lamp 504, a left front lamp 506, abumper frame 508, bumper support members 510, 512, linear motion pipes514, 516, coil springs 518, 520, linear motion bearings 522, 524 (seeFIG. 28 ), abutment plates 526, 528 (see FIG. 29 ), and collisiondetection switches 530, 532 (see FIG. 29 ).

The base member 500 is fixed to the front support member 22 of thecarriage unit 4 (see FIG. 2 ). As shown in FIG. 27 , the housing 502 isfixed to the base member 500. The housing 502 includes a housing unit502 a having a substantially rectangular box shape with its longitudinaldirection along the left-right direction, a right support portion 502 barranged at a right end of the housing unit 502 a, and a left supportportion 502 c arranged at a left end of the housing unit 502 a. Theright front lamp 504 is fixed to the right support portion 502 b. Theleft front lamp 506 is fixed the left support portion 502 c. The rightfront lamp 504 and the left front lamp 506 respectively emit light infront of the cart 2. The right front lamp 504 and the left front lamp506 are respectively electrically connected to the main control circuitboard 44 (see FIG. 9 ).

The bumper frame 508 is constituted of a round steel pipe. The bumpersupport members 510, 512 are respectively arranged rearward from thebumper frame 508, and are fixed to the bumper 508. The bumper supportmember 510 is attached to the linear motion pipe 514 by bolts 534 a, 534b and nuts 536 a, 536 b (see FIG. 28 ). The bumper support member 512 isattached to the linear motion pipe 516 by bolts 538 a, 538 b and nuts540 a, 540 b.

As shown in FIG. 28 , the linear motion pipe 514 is arranged with itslongitudinal direction along the front-rear direction. Elongated holes514 a, 514 b arranged adjacent to each other in the front-rear directionand respectively having their longitudinal directions along thefront-rear direction are defined in the vicinity of a front end of thelinear motion pipe 514. A bolt 534 a penetrates the elongated hole 514 aand a bolt 534 b penetrates the elongated hole 514 b. Due to this, thebumper support member 510 is supported by the linear motion pipe 514 soas to be movable in the front-rear direction between a position at whichthe bolts 534 a, 534 b contact front edges of the elongated holes 514 a,514 b and a position at which the bolts 534 a, 534 b contact rear edgeof the elongated holes 514 a, 514 b. Similarly, the linear motion pipe510 is arranged with its longitudinal direction along the front-reardirection. Elongated holes 516 a, 516 b arranged adjacent to each otherin the front-rear direction and respectively having their longitudinaldirections along the front-rear direction are defined the vicinity of afront end of the linear motion pipe 516. A bolt 538 a penetrates theelongated hole 516 a and a bolt 538 b penetrates the elongated hole 516b. Due to this, the bumper support member 512 is supported by the linearmotion pipe 516 so as to be movable in the front-rear direction betweena position at which the bolts 538 a, 538 b contact front edges of theelongated holes 516 a, 516 b and a position at which the bolts 538 a,538 b contact rear edges of the elongated holes 516 a, 516 b.

Rear ends of the linear motion pipes 514, 516 penetrate front walls ofthe base member 500 and the housing 502 and enter into the housing 502.The linear motion pipes 514, 516 are supported by the linear motionbearings 522, 524 in the vicinity of their rear ends so as to be movablein the front-rear direction. The linear motion bearings 522, 524 arefixed to the front wall of the housing 502. The coil springs 518, 520are attached to the linear motion pipes 514, 516. Front ends of the coilsprings 518, 520 abut tear surfaces of the bumper support members 510,512, and rear ends of the coil springs 518, 520 abut a front surface ofthe base member 500. The coil springs 518, 520 bias the bumper supportmembers 510, 512 frontward relative to the base member 500.

As shown in FIG. 29 , the abutment plates 526, 528 are fixed to the rearends of the linear motion pipes 514, 516. The abutment plates 526, 528respectively include abutment portions 526 a, 528 a that extend radiallyoutward. The collision detection switches 530, 532 are arranged in frontof the abutment portions 526 a, 528 a. In a state where an externalforce is not applied to the bumper frame 508, the linear motion pipes514, 516 are located forward relative to the housing 502 by the biasingforces of the coil springs 518, 520. In this case the abutment portions526 a, 528 a are in abutment with the collision detection switches 530,532, by which the collision detection switches 530, 532 are in anoff-state. When a backward external force is applied to the bumper frame508, the linear motion pipes 514, 516 move backward relative to thehousing 502 against the biasing forces of the coil springs 518, 520. Inthis case, abutment portions 526 a, 528 a separate from the collisiondetection switches 530, 532, by which the collision detection switches530, 532 shift to an on-state. The collision detection switches 530, 532are respectively electrically connected to the main control circuitboard 44 (see FIG. 9 ).

(Circuit Configuration of Cart 2)

As shown in FIG. 30 , the control power supply circuit 432 iselectrically connected to the main power switch 96. The control powersupply circuit 432 is configured to allow power supply from the batterypack 38 when an on-operation is performed on the main power switch 96,and prohibit the power supply from the battery pack 38 when anoff-operation is performed on the main power switch 96. When main powerof the cart 2 is in an on-state, the control power supply circuit 432supplies the power from the battery pack 38 to the shutoff circuits 438,440, 442 without stepping it down from the voltage (Vbat) of the batterypack 38. Further, when the main power of the cart 2 is in the on-state,the power supply circuit 432 steps down the power from the battery pack38 from the voltage (Vbat) of the battery pack 38 to a predeterminedvoltage (Vcc) and supplies the same to respective electronic componentssuch as the main MCU 434, the switch circuit 436, the automatic drivingMCU 430, and the motor MCUs 444, 446, 448, 450, 452. Hereinbelow, apotential of the voltage (Vbat) of the battery pack 38 may be termed abattery potential, and a potential of the voltage (Vcc) stepped down bythe control power supply circuit 432 may termed a power supplypotential.

The main MCU 434 is configured to control overall operations of the cart2. The main power switch 96, the speed shifter switch 104, the hornswitch 106, the LEDs 476, the buzzer 478, the steering angle sensor 166,the overload detection sensors 320 a, 320 b, 320 c, 320 d, the rightfront lamp 504, and the left front lamp 506 are electrically connectedto the main MCU 434. Further, the mode shifter switch 98, the triggerswitch 100, the travelling direction shifter switch 102, the emergencystop switch 308, the collision detection switches 530, 532, and therotation angle sensor 88 are electrically connected to the main MCU 434via the switch circuit 436. Further, the wireless I/F 428 iselectrically connected to the main MCU 434 via the automatic driving MCU430. The automatic driving MCU 430 is configured to generate atravelling route which the cart 2 should realize in a tracking operationand in the remote control operation performed by the cart 2 under theautomatic mode based on signals from the wireless I/F 428 and outputsthe same to the main MCU 434 as command values.

The motor MCUs 444, 446, 448, 450, 452 are electrically connected to themain MCU 434. The motor MCU 444 is configured to control operations ofthe right front wheel motor 232 through the motor driver 454, and alsocontrol operations of the brake circuit 468 and the cooling fan 50 d.The motor MCU 446 is configured to control operations of the left frontwheel motor 242 through the motor driver 456, and also controloperations of the brake circuit 470 and the cooling fan 52 d. The motorMCU 448 is configured to control operations of the right rear wheelmotor 486 through the motor driver 458, and also control operations ofthe brake circuit 472 and the cooling fan 54 d. Further, the motor MCU448 is configured to control operations of the right rear wheelelectromagnetic brake 490 through the electromagnetic brake driver 464.The motor MCU 450 is configured to control operations of the left rearwheel motor 492 through the motor driver 460, and also controloperations of the brake circuit 474 and the cooling fan 56 d. Further,the motor MCU 450 is configured to control operations of the left rearwheel electromagnetic brake 496 through the electromagnetic brake driver466. The motor MCU 452 is configured to control operations of thesteering motor 176 through the motor driver 462.

The shutoff circuit 438 is arranged on an electric power supply pathfrom the control power supply circuit 432 to the motor drivers 454, 456,458, 460. The shutoff circuit 438 is configured to switch between astate allowing power supply from the control power supply circuit 432 tothe motor drivers 454, 456, 458, 460 and a state prohibiting to do so.The shutoff circuit 440 is arranged on an electric power supply pathfront the control power supply circuit 432 to the electromagnetic brakedrivers 464, 466. The shutoff circuit 440 is configured to switchbetween a state allowing power supply from the control power supplycircuit 432 to the electromagnetic brake drivers 464, 466 and a stateprohibiting to do so. The shutoff circuit 442 is arranged on an electricpower supply path from the control power supply circuit 432 to the motordriver 462. The shutoff circuit 442 is configured to switch between astate allowing power supply from the control power supply circuit 432 tothe motor driver 462 and a state prohibiting to do so. Each of theshutoff circuits 438, 440, 442 is electrically connected to the main MCU434 and the switch circuit 436.

(Configuration of Switch Circuit 436)

As shown in FIG. 31 , the switch circuit 436 includes cancel circuits542, 544, 546, a delay circuit 548, AND gates 550, 552, OR gates 554,556, NOT gates 558, 560, 562, 564, 566, and resistors 568, 570, 572,574, 576, 578.

The mode shifter switch 98 includes a ground terminal 98 a, a manualmode terminal 98 b, and an automatic mode terminal 98 c. The groundterminal 98 a is connected to a ground potential. The manual modeterminal 98 b is connected to the power supply potential via theresistor 568, and is connected to the main MCU 434. The automatic modeterminal 98 c is connected to the power supply potential via theresistor 570, and is connected to the main MCU 434.

When the user selects die manual mode in the mode shifter switch 98, theground terminal 98 a and the manual mode terminal 98 b becomeelectrically conducted and the ground terminal 98 a and the automaticmode terminal 98 c become electrically non-conducted. In this case, themanual mode terminal 98 b comes to have L potential and the automaticmode terminal 98 c comes to have H potential. When an input from themanual mode terminal 98 b becomes L potential, the main MCU 434recognizes that the manual mode has been selected by the user. When theuser selects the automatic mode in the mode shifter switch 98, theground terminal 98 a and the manual mode terminal 98 b becomeelectrically non-conducted and the ground terminal 98 a and theautomatic mode terminal 98 c become electrically conducted. In thiscase, the manual mode terminal 98 b comes to have H potential and theautomatic mode terminal 98 c comes to have L potential. When an inputfrom the automatic mode terminal 98 c becomes L potential, the main MCU434 recognizes that the automatic mode has been selected by the user.When the user selects the parking mode in the mode shifter switch 98,the ground terminal 98 a and the manual mode terminal 98 b becomeelectrically non-conducted and the ground terminal 98 a and theautomatic mode terminal 98 c also become electrically non-conducted. Inthis case, the manual mode terminal 98 b comes to have H potential, andthe automatic mode terminal 98 c also comes to have H potential. Whenthe inputs from the manual mode terminal 98 b and the automatic modeterminal 98 c both become H potential, the main MCU 434 recognizes thatthe parking mode has been selected by the user.

The cancel circuit 542 includes a transistor 542 a and resistors 542 b,542 c, 542 d. The transistor 542 a is a PNP transistor. The resistor 542b has its one end connected to an emitter of the transistor 542 a andits other end connected to a base of the transistor 542 a. The resistor542 c has its one end connected to the base of the transistor 542 a andits other end connected to the automatic mode terminal 98 c of the modeshifter switch 98. The resistor 542 d has its one end connected to therotation angle sensor 88 and its oilier end connected to a collector ofthe transistor 542 a. Further, the emitter of the transistor 542 a isconnected to the power supply potential, and the collector of thetransistor 542 a is connected to the main MCU 434.

The rotation angle sensor 88 is configured to output a potentialcorresponding to a rotation angle to the cancel circuit 542. When theautomatic mode terminal 98 c has H potential, the transistor 542 a is inan off-state and the potential outputted from the rotation angle sensor88 is inputted to the main MCU 434. When the automatic mode terminal 98c has L potential, the transistor 542 a is in an on-state and Hpotential is inputted to the main MCU 434 regardless of the potentialoutputted from the rotation angle sensor 88. That is, the cancel circuit542 is configured to cancel an input signal from the rotation anglesensor 88 when the automatic mode is selected in the mode shifter switch98.

The trigger switch 100 includes a ground terminal 100 a, a triggerterminal 100 b, and a variable resistor 100 c. The ground terminal 100 ais connected to the ground potential. The trigger terminal 100 b isconnected to the power supply potential via, the resistor 572. When theuser has not operated the trigger switch 100 to turn it on, the groundterminal 100 a and the trigger terminal 100 b are electricallynon-conducted, and thus the trigger terminal 100 b has H potential. Whenthe user has operated the trigger switch 100 to turn it on, the groundterminal 100 a and the trigger terminal 100 b are electricallyconducted, and thus the trigger terminal 100 b has L potential. Thevariable resistor 100 c of the trigger switch 100 has its one endconnected to the ground potential and its other end connected to thepower supply potential, and is configured to output a potentialcorresponding to an amount of a pressing operation performed by the userupon turning on the trigger switch 100 to the cancel circuit 544.

The cancel circuit 544 includes a transistor 544 a and resistors 544 b,544 c, 544 d. The transistor 544 a is a PNP transistor. The resistor 544b has its one end connected to an emitter of the transistor 544 a andits other end connected to a base of the transistor 544 a. The resistor544 c has its one end connected to the base of the transistor 544 a andits other end connected to the automatic mode terminal 98 c of the modeshifter switch 98. The resistor 544 d has its one end connected to thevariable resistor 100 c of the trigger switch 100 and its other endconnected to a collector of the transistor 544 a. Further, the emitterof the transistor 544 a is connected to the power supply potential, andthe collector of the transistor 544 a is connected to the main MCU 434.

When the automatic mode terminal 98 c has H potential, the transistor544 a is off and the potential outputted from the variable resistor 100c is inputted to the main MCU 434. In this case, the main MCU 434recognizes the operation performed by the user on the trigger switch 100based on the potential outputted from the variable resistor 100 c. Whenthe automatic mode terminal 98 c has L potential, the transistor 544 ais on and H potential is inputted to the main MCU 434 regardless of thepotential outputted from the variable resistor 100 c. That is, thecancel circuit 544 cancels the input signal from the variable resistor100 c of the trigger switch 100 when the automatic mode is selected inthe mode shifter switch 98.

The trigger terminal 100 b of the trigger switch 100 is connected to afirst input terminal of the OR gate 554 via the NOT gate 558. Theautomatic mode terminal 98 c of the mode shifter switch 98 is connectedto a second input terminal of the OR gate 554 via the NOT gate 560. Anoutput terminal of the OR gate 554 is connected to a first inputterminal of the AND gate 550. An output terminal of the AND gate 550 isconnected to the shutoff circuit 438. As will be described later, theshutoff circuit 438 is configured to: allow power supply to the motordrivers 454, 456, 458, 460 when the output terminal of the AND gate 550has H potential; and shut off the power supply to the motor drivers 454,456, 458, 460 when the output terminal of the AND gate 550 has Lpotential.

As will be described later, a second input terminal of the AND gate 550normally has H potential inputted therein. In this case, when theautomatic mode terminal 98 c has H potential, the output terminal of theOR gate 554 and the output terminal of the AND gate 550 have L potentialif the trigger terminal 100 b has H potential, and the output terminalof the OR gate 554 and the output terminal of the AND gate 550 have Hpotential if the trigger terminal 100 b has L potential. Due to this,when the automatic mode is not selected in the mode shifter switch 98, Hpotential is inputted to the shutoff circuit 438 if the trigger switch100 is operated to an on-state, and L potential is inputted to theshutoff circuit 438 if the trigger switch 100 is not operated to theon-state. On the other hand, when the automatic mode terminal 98 c haspotential, the output terminal of the OR gate 554 and the outputterminal of the AND gate 550 have H potential regardless of thepotential of the trigger terminal 100 b. Due to this, when the automaticmode is selected in the mode shifter switch 98, H potential is inputtedfrom the switch circuit 436 to the shutoff circuit 438 regardless ofwhether the trigger switch 100 is operated to the on-state.

The output terminal of the AND gate 550 is also connected to an inputterminal of the delay circuit 548. An output terminal of the delaycircuit 548 is connected to the shutoff circuit 440. As will bedescribed later, the shutoff circuit 440 is configured to: allow powersupply to the electromagnetic brake drivers 464, 466 when the outputterminal of the delay circuit 548 has H potential; and shut off thepower supply to the electromagnetic brake drivers 464, 466 when theoutput terminal of the delay circuit 548 has L potential. The delaycircuit 548 includes a diode 548 a, a resistor 548 b, a capacitor 548 c,and a buffer gate 548 d. An anode of the diode 548 a is connected to aninput terminal of the delay circuit 548. A cathode of the diode 548 a isconnected to an input terminal of the buffer gate 548 d. The resistor548 b has its one end connected to a cathode of the diode 548 a and itsother end connected to the ground potential. The capacitor 548 c has itsone end connected to the cathode of the diode 548 a and its other endconnected to the ground potential. An output terminal of the buffer gate548 d is connected to the output terminal of the delay circuit 548. In acase where the output terminal of the AND gate 550 shifts from Lpotential to H potential, the output terminal of the delay circuit 548also shifts from L potential to H potential after a predetermined delaytime that is set according to a time constant of the resistor 548 b andthe capacitor 548 c has elapsed. Further, in a case where the outputterminal of the AND gate 550 shifts from H potential to L potential, theoutput terminal of the delay circuit 548 also shifts from H potential toL potential after the predetermined delay time that is set according tothe time constant of the resistor 548 b and the capacitor 548 c haselapsed.

The emergency stop switch 308 includes a ground terminal 308 a and anemergency stop terminal 308 b. The ground terminal 308 a is connected tothe ground potential. The emergency stop terminal 308 b is connected tothe power supply potential via the resistor 574, and is connected to themain MCU 434. When the emergency stop switch 308 is off, the groundterminal 308 a and the emergency stop terminal 308 b are electricallyconducted and the emergency stop terminal 308 b thereby comes to have Lpotential. When the emergency stop switch 308 is on, the ground terminal308 a and the emergency stop terminal 308 b are electricallynon-conducted and the emergency stop terminal 308 b thereby comes tohave H potential. When an input from the emergency stop terminal 308 bbecomes H potential, the main MCU 434 recognizes that the emergency stopswitch 308 has been turned on by the user.

The collision detection switch 530 includes a ground terminal 530 a anda collision detection terminal 530 b. The collision detection switch 532includes a ground terminal 532 a and a collision detection terminal 532b. The ground terminal 530 a is connected to the ground potential. Thecollision detection terminal 530 b is connected to the ground terminal532 a. The collision detection terminal 532 b is connected to the powersupply potential via the resistor 576, and is connected to the main MCU434. When the collision detection switch 530 is off, the ground terminal530 a and the collision detection terminal 530 b are electricallyconducted, and when the collision detection switch 530 is on, the groundterminal 530 a and the collision detection terminal 530 b areelectrically non-conducted. When the collision detection switch 532 isoff, the ground terminal 532 a and the collision detection terminal 532b are electrically conducted, and when the collision detection switch532 is on, the ground terminal 532 a and the collision detectionterminal 532 b are electrically non-conducted. Due to this, thecollision detection terminal 532 b has L potential. When both thecollision detection switches 530, 532 are off, and the collisiondetection terminal 532 b has H potential when one of or both of thecollision detection switches 530, 532 are off. The main MCU 434recognizes that a collision has been detected by the collision detectionswitches 530, 532 when an input form the collision detection terminal532 b becomes H potential.

The travelling direction shifter switch 102 includes a ground terminal102 a and a travelling direction terminal 102 b. The ground terminal 102a is connected to the ground potential. The travelling directionterminal 102 b is connected to the cancel circuit 546. In the travellingdirection shifter switch 102, when the forward motion is selected by theuser, the ground terminal 102 a and the travelling direction terminal102 b are electrically non-conducted, and when the backward motion isselected by the user, the ground terminal 102 a and the travellingdirection terminal 102 b are electrically conducted.

The cancel circuit 546 includes a transistor 546 a and resistors 546 b,546 c, 546 d. The transistor 546 a is a PNP transistor. The resistor 546b has its one end connected to an emitter of the transistor 546 a andits other end connected to a base of the transistor 546 a. The resistor546 c has its one end connected to the base of the transistor 546 a andits other end connected to the automatic mode terminal 98 c of the modeshifter switch 98. The resistor 546 d has its one end connected to thetravelling direction terminal 102 b of the travelling direction shifterswitch 102 and its other end connected to a collector of the transistor546 a. Further, the emitter of the transistor 546 a is connected to thepower supply potential, and the collector of the transistor 546 a isconnected to the power supply potential via the resistor 578, and isconnected to the main MCU 434.

When the automatic mode terminal 98 c has H potential, the transistor546 a is off, and the collector of the transistor 546 a has H potentialif the forward motion is selected in the travelling direction shifterswitch 102, and the collector of the transistor 546 a has L potential ifthe backward motion is selected in the travelling direction shifterswitch 102. In this case, the main MCU 434 recognizes which one of theforward motion and the backward motion is selected based on a potentialthat is inputted therein. When the automatic mode terminal 98 c has Lpotential, the transistor 546 a turns on and the collector of thetransistor 546 a becomes H potential regardless of which one of theforward motion and the backward motion is selected in the travellingdirection shifter switch 102. That is, when the automatic mode isselected in the mode shifter switch 98, the cancel circuit 546 cancelsthe input signals from the travelling direction shifter switch 102.

The emergency stop terminal 308 b of the emergency stop switch 308 isconnected to a first input terminal of the AND gate 552 via the NOT gate562. The collision detection terminal 532 b of the collision detectionswitch 532 is connected to a first input terminal of the OR gate 556 viathe NOT gate 562. The collector of the transistor 546 a of the cancelcircuit 546 is connected to a second input terminal of the OR gate 556via the NOT gate 564. An output terminal of the OR gate 556 is connectedto a second input terminal of the AND gate 552. An output terminal ofthe AND gate 552 is connected to the second input terminal of the ANDgate 550 and also to the shutoff circuit 442. As will be describedlater, the shutoff circuit 442 is configured to: allow power supply tothe motor driver 462 when the output terminal of the AND gate 552 has Hpotential; and shut off the power supply to the motor driver 462 whenthe output terminal of the AND gate 552 has L potential.

When the emergency stop terminal 308 b has H potential, the outputterminal of the AND gate 552 has L potential regardless of the potentialof the OR gate 556. Due to this, when the emergency stop switch 308 isarmed on, L potential is inputted to the second input terminal of theAND gate 550 and also L potential is inputted from the switch circuit436 to the shutoff circuit 442 regardless of the states of the modeshifter switch 98, the collision detection switches 530, 532, and thetravelling direction shifter switch 102.

When the emergency stop terminal 308 b has L potential and L potentialis inputted to the second input terminal of the OR gate 556, the outputterminal of the OR gate 556 and the output terminal of the AND gate 552come to have H potential if the collision detection terminal 532 b has Lpotential, and on the other hand the output terminal of the OR gate 556and the output terminal of the AND gate 552 come to have L potential ifthe collision detection terminal 532 b has H potential. Due to this, thesecond input terminal of the AND gate 550 has H potential when nocollision is detected by the collision detection switches 530, 532, andH potential is inputted from the switch circuit 436 to the shutoffcircuit 442. When a collision is detected by the collision detectionswitches 530, 532, L potential is inputted to the second input terminalof the AND gate 550 and L potential is inputted from the switch circuit436 to the shutoff circuit 442. That is, the collision detection by thecollision detection switches 530, 532 is activated.

When the emergency stop terminal 308 b has L potential and H potentialis inputted to the second input terminal of the OR gate 556, the outputterminal of the OR gate 556 and the output terminal of the AND gate 552come to have H potential regardless of the potential of the collisiondetection terminal 532 b. Due to this, H potential is inputted to thesecond input terminal of the AND gate 550 regardless of the states ofthe collision detection switches 530, 532, and H potential is inputtedfrom the switch circuit 436 to the shutoff circuit 442. That is, thecollision detection by the collision detection switches 530, 532 isdisabled.

When the automatic mode terminal 98 c has H potential, since thetransistor 546 a of the cancel circuit 546 is off, L potential isinputted to the second input terminal of the OR gate 556 if thetravelling direction terminal 102 b has H potential, and H potential isinputted to the second input terminal of the OR gate 556 if thetravelling direction terminal 102 b has L potential. That is, in thestate where the automatic mode is not selected in the mode shifterswitch 98, the collision detection of the collision detection switches530, 532 is activated if the forward motion is selected in thetravelling direction shifter switch 102, and the collision detection ofthe collision detection switches 530, 532 is disabled if the backwardmotion is selected in the travelling direction shifter switch 102.

When the automatic mode terminal 98 c has L potential, L potential isinputted to the second input terminal of the OR gate 556 regardless ofthe potential of the travelling direction terminal 102 b since thetransistor 546 a of the cancel circuit 546 is turned on. That is, whenthe automatic mode is selected in the mode shifter switch 98, thecollision detection of the collision detection switches 530, 532 isenabled regardless of the state of the travelling direction shifterswitch 102.

(Configuration of Shutoff Circuit 438)

As shown in FIG. 32 , the shutoff circuit 438 includes a switchingelement 438 a, a driver IC 438 b, and an AND gate 438 c. The switchingelement 438 a is for example a field effect transistor, and may morespecifically be a n-channel MOSFET having an insulated gate. A drain ofthe switching element 438 a is connected to the battery potential (Vbat)output of the control power supply circuit 432, a source of theswitching element 438 a is connected to the motor drivers 454, 456, 458,460, and a gate of the switching element 438 a is connected to thedriver IC 438 b. A first input terminal of the AND gate 438 c isconnected to the switch circuit 436, a second input terminal of the ANDgate 438 c is connected to the main MCU 434, and an output terminal ofthe AND gate 438 c is connected to the driver IC 438 b. The driver IC438 b is configured to electrically conduct the switching element 438 awhen the output terminal of the AND gate 438 c has H potential, that is,when both the first input terminal and the second input terminal of theAND gate 438 c have H potential. The driver IC 438 b is configured notto electrically conduct the switching element 438 a when the outputterminal of the AND gate 438 c has L potential, that is, when one of orboth the first input terminal and the second input terminal of the ANDgate 438 c have L potential.

(Configuration of Motor Drivers 454, 456, 458, 460)

The motor drivers 454, 456, 458, 460 are respectively connected to theircorresponding one of the right front wheel motor 232, the left frontwheel motor 242, the right rear wheel motor 486, and the left rear wheelmotor 492 via U-phase, V-phase, and W-phase output terminals. Further,the motor drivers 454, 456, 458, 460 are respectively connected to thebrake circuits 468, 470, 472, 474 via brake circuit output terminals.

The motor drivers 454, 456, 458, 460 each include a first switchingelement 454 a, 456 a, 458 a, 460 a, a second switching element 454 b,456 b, 458 b, 460 b, a third switching element 454 c, 456 c, 458 c, 460c, a fourth switching element 454 d, 456 d, 458 d, 460 d, a fifthswitching element 454 e, 456 e, 458 e, 460 e, a sixth switching element454 f, 456 f, 458 f, 460 f, a first diode 454 g, 456 g, 458 g, 460 g, asecond diode 454 h, 456 h, 458 h, 460 h, and a third diode 454 i, 456 i,458 i, 460 i. Each of these first switching elements 454 a, 456 a, 458a, 460 a, second switching elements 454 b, 456 b, 458 b, 460 b, thirdswitching elements 454 c, 456 c, 458 c, 460 c, fourth switching elements454 d, 456 d, 458 d, 460 d, fifth switching elements 454 e, 456 e, 458e, 460 e, and sixth switching elements 454 f, 456 f, 458 f, 460 f mayfor example be field effect transistors, and may more specifically ben-channel MOSFETs having insulated gates.

A drain of each of the first switching elements 454 a, 456 a, 458 a, 460a is connected to the source of the switching element 438 a in theshutoff circuit 438, a source of each of the first switching elements454 a, 456 a, 458 a, 460 a is connected to the U-phase output terminal,and a gate of each of the first switching elements 454 a, 456 a, 458 a,460 a is connected to its corresponding motor MCU 444, 446, 448, 450. Adrain of each of the second switching elements 454 b, 456 b, 458 b, 460b is connected to the U-phase output terminal, a source of each of thesecond switching elements 454 b, 456 b, 458 b, 460 b is connected to theground potential, and a gate of each of the second switching elements454 b, 456 b, 458 b, 460 b is connected to its corresponding motor MCU444, 446, 448, 450.

A drain of each of the third switching elements 454 c, 456 c, 458 c, 460c is connected to the source of the switching element 438 a in theshutoff circuit 438, a source of each of the third switching elements454 c, 456 c, 458 c, 460 c is connected to the V-phase output terminal,and a gate of each of the third switching elements 454 c, 456 c, 458 c,460 c is connected to its corresponding motor MCU 444, 446, 448, 450. Adrain of each of the fourth switching elements 454 d, 456 d, 458 d, 460d is connected to the V-phase output terminal, a source of each of thefourth switching elements 454 d, 456 d, 458 d, 460 d is connected to theground potential, and a gate of each of the fourth switching elements454 d, 456 d, 458 d, 460 d is connected to its corresponding motor MCU444, 446, 448, 450.

A drain of each of the fifth switching elements 454 c, 456 e, 458 e, 460e is connected to the source of the switching element 438 a in theshutoff circuit 438, a source of each of the fifth switching elements454 e, 456 e, 458 e, 460 e is connected to the W-phase output terminal,and a gate of each of the fifth switching elements 454 e, 456 e, 458 e,460 e is connected to its corresponding motor MCU 444, 446, 448, 450. Adrain of each of the sixth switching elements 454 f, 456 f, 458 f, 460 fis connected to the W-phase output terminal, a source of each of thesixth switching elements 454 f, 456 f, 458 f, 460 f is connected to theground potential, and a gate of each of the sixth switching elements 454f, 456 f, 458 f, 460 f is connected to its corresponding motor MCU 444,446, 448, 450.

Detection signals of the Hall sensors 482, 484, 488, 494 of the rightfront wheel motor 232, the left front wheel motor 242, the right rearwheel motor 486, and the left rear wheel motor 492 are respectivelyinputted to the motor MCUs 444, 446, 448, 450. The motor MCUs 444, 446,448, 450 are configured to operate their corresponding one of the rightfront wheel motor 232, the left front wheel motor 242, the right rearwheel motor 486, and the left rear wheel motor 492 at their desiredrotation speeds by switching on/off of the first switching elements 454a, 456 a, 458 a, 460 a, the second switching elements 454 b, 456 b, 458b, 460 b, the third switching elements 454 c, 456 c, 458 c, 460 c, thefourth switching elements 454 d, 456 d, 458 d, 460 d, the fifthswitching elements 454 e, 456 e, 458 e, 460 e, and the sixth switchingelements 454 f, 456 f, 458 f, 460 f in accordance with the detectionsignals from the Hall sensors 482, 484, 488, 494. Further, the motorMCUs 444, 446, 448, 450 are configured to apply brake to the rotation oftheir corresponding one of the right front wheel motor 232, the leftfront wheel motor 242, the right rear wheel motor 486, and the left rearwheel motor 492, with a so-called short brake by switching the secondswitching element 454 b, 456 b, 458 b, 460 b, the fourth switchingelement 454 d, 456 d, 458 d, 460 d, and the sixth switching element 454f, 456 f, 458 f, 460 f to on.

An anode of each of the first diodes 454 g, 456 g, 458 g, 460 g isconnected to the U-phase output terminal, and a cathode of each of thefirst diodes 454 g, 456 g, 458 g, 460 g is connected to the brakecircuit output terminal. An anode of each of the second diodes 454 h,456 h, 458 h, 460 h is connected to the V-phase output terminal, and acathode of each of the second diodes 454 h, 456 h, 458 h, 460 h isconnected to the brake circuit output terminal. A anode of each of thethird diodes 454 i, 456 i, 458 i, 460 i is connected to the W-phaseoutput terminal, and a cathode of each of the third diodes 454 i, 456 i,458 i, 460 i is connected to the brake circuit output terminal.

(Configuration of Brake Circuits 468, 470, 472, 474)

The brake circuits 468, 470, 472, 474 each include a switching element468 a, 470 a, 472 a, 474 a, a resistor 468 b, 470 b, 472 b, 474 b, anamplifier 468 c, 470 c, 472 c, 474 c, an operational amplifier 468 d,470 d, 472 d, 474 d, and a thermistor 468 e, 470 e, 472 e, 474 e.

The switching elements 468 a, 470 a, 472 a, 474 a may for example befield effect transistors, and may more specifically be n-channel MOSFETswith insulated gates. A drain of each of the switching elements 468 a,470 a, 472 a, 474 a is connected to the brake circuit output terminal ofthe corresponding motor driver 454, 456, 458, 460, a source of each ofthe switching elements 468 a, 470 a, 472 a, 474 a is connected to theground potential via the corresponding resistor 468 b, 470 b, 472 b, 474b, and a gate of each of the switching elements 468 a, 470 a, 472 a, 474a is connected to an output terminal of the corresponding operationalamplifier 468 d, 470 d, 472 d, 474 d. The switching elements 468 a, 470a, 472 a, 474 a are configured to operate in a linear mode or in aswitching mode in accordance with a gate voltage level. In the linearmode, drain current changes substantially linearly when a gate voltagechanges, and in the switching mode, the drain current does not change somuch even when the gate voltage changes.

The amplifiers 468 c, 470 c, 472 c, 474 c are each configured to detecta voltage between one end and another end of the corresponding resistor468 b, 470 b, 472 b, 474 b, amplify the detected voltage, and output thesame to an inverting input terminal of the corresponding operationalamplifier 468 d, 470 d, 472 d, 474 d. Non-inverting input terminals ofthe operational amplifiers 468 d, 470 d, 472 d, 474 d are each connectedto the corresponding motor MCU 444, 446, 448, 450. The operationalamplifiers 468 d, 470 d, 472 d, 474 d are each configured to apply avoltage, which corresponds to a difference between a current commandvalue inputted from the motor MCU 444, 446, 448, 450 to thenon-inverting input terminal and a current detection value inputted fromthe amplifier 468 c, 470 c, 472 c, 474 c to the inverting inputterminal, to the gate of the switching element 468 a, 470 a, 472 a, 474a. Due to this the switching element 468 a, 470 a, 472 a, 474 a operatesin the linear mode, and the operation of the switching element 468 a,470 a, 472 a, 474 a is controlled so that current in accordance with thecurrent command value from the motor MCU 444, 446, 448, 450 flows in theresistor 468 b, 470 b, 472 b, 474 b. That is, the brake circuits 468,470, 472, 474 can each be said as being a linear regulator.

When large current flows from the motor drivers 454, 456, 458, 460 tothe brake circuits 468, 470, 472, 474 while the right front wheel motor232, the left front wheel motor 242, the right rear wheel motor 486, andthe left rear wheel motor 492 are rotating, strong braking forces areapplied to the right front wheel motor 232, the left front wheel motor242, the right rear wheel motor 486, and the left rear wheel motor 492.Due to this, the motor MCUs 444, 446, 448, 450 can cause large brakingforces to be applied to the right front wheel motor 232, the left frontwheel motor 242, the right rear motor 486, and the left rear wheel motor492 by the brake circuits 468, 470, 472, 474 while the right front wheelmotor 232, the left front wheel motor 242, the right rear wheel motor486, and the left rear wheel motor 492 are rotating.

When the braking farces are applied to the right front wheel motor 232,the left front wheel motor 242, the right rear wheel motor 486, and theleft rear wheel motor 492 by the brake circuits 468, 470, 472, 474,large current flows in the switching elements 468 a, 470 a, 472 a, 474 aand the resistors 468 b, 470 b, 472 b, 474 b, as a result of whichtemperatures of the brake circuits 468, 470, 472, 474 rise due to heatgeneration. Due to this, when the brake circuits 468, 470, 472, 474 areto be operated, the motor MCUs 444, 446, 448, 450 actuate the coolingfans 50 d, 52 d, 54 d, 56 d to cool the brake circuits 468, 470, 472474.Further, the motor MCUs 444, 446, 448, 450 have the thermistors 468 e,470 e, 472 e, 474 e connected thereto. The thermistors 468 e, 470 e, 472e, 474 e are configured to detect the temperatures of the brake circuits468, 470, 472, 474 and output the same to the motor MCUs 444, 446, 448,450.

In each of the brake circuits 468, 470, 472, 474, multiple sets (such assix sets) of the switching element 468 a, 470 a, 472 a, 474 a, theresistor 468 b, 470 b, 472 b, 474 b, the amplifier 468 c, 470 c, 472 c,474 c, the operational amplifier 468 d, 470 d, 472 d, 474 d, and thethermistor 468 e, 470 e, 472 e, 474 e may be prepared, and these setsmay be connected to each other in parallel. By configuring as such, evenlarger current can be supplied from the motor drivers 454, 456, 458, 460to the brake circuits 468, 470, 472, 474, and larger braking forces canbe applied to the right front wheel motor 232, the left front wheelmotor 242, the right rear wheel motor 486, and the left rear wheel motor492.

(Configuration of Shutoff Circuit 440)

As shown in FIG. 33 , the shutoff circuit 440 includes a switchingelement 440 a, a driver IC 440 b, and an AND gate 440 c. The switchingelement 440 a may for example be a field effect transistor, and may morespecifically be a n-channel MOSFET with an insulated gate. A drain ofthe switching element 440 a is connected to the battery potential (Vbat)output of the control power supply circuit 432, a source of theswitching element 440 a is connected to the electromagnetic brakedrivers 464, 466, and a gate of the switching element 440 a is connectedto the driver IC 440 b. A first input terminal of the AND gate 440 c isconnected to the switch circuit 436, a second input terminal of the ANDgate 440 c is connected to the main MCU 434, and an output terminal ofthe AND gate 440 c is connected to the driver IC 440 b. The driver IC440 b is configured to electrically conduct the switching element 440 awhen the output terminal of the AND gate 440 c has H potential, that is,when both the first and second input terminals of the AND gate 440 chave H potential. The driver IC 440 b is configured not to electricallyconduct the switching element 440 a when the output terminal of the ANDgate 440 c has L potential, that is, when one of or both of the firstand second input terminals of the AND gate 440 c have L potential.

(Configuration of Electromagnetic Brake Drivers 464, 466)

The electromagnetic brake drivers 464, 466 are respectively connected tothe right rear wheel electromagnetic brake 490 and the left rear wheelelectromagnetic brake 496 via positive and negative output terminals.The electromagnetic brake drivers 464, 466 each include a switchingelement 464 a, 466 a and a diode 464 b, 466 b.

The switching elements 464 a, 466 a may for example be field effecttransistors, and may more specifically be n-channel MOSFETs withinsulated gates. A drain of each of the switching elements 464 a, 466 ais connected to the negative output terminal, a source of each of theswitching elements 464 a, 466 a is connected to the ground potential,and a gate of each of the switching elements 464 a, 466 a is connectedto the corresponding motor MCU 448, 450. An anode of each of the diodes464 b, 466 b is connected to the negative output terminal, and a cathodeof each of the diodes 464 b, 466 b is connected to the positive outputterminal.

The right rear wheel electromagnetic brake 490 and the left rear wheelelectromagnetic brake 496 are configured to: apply the braking forces tothe right rear wheel motor 486 and the left rear wheel motor 492 when novoltage is applied between the positive and negative output terminals;and release the braking forces on the right rear wheel motor 486 and theleft rear wheel motor 492 when a voltage is applied between the positiveand negative output terminals. When the motor MCUs 448, 450 turn on theswitching elements 464 a, 466 a of the electromagnetic brake drivers464, 466 while the switching element 440 a of the shutoff circuit 440 isin the on-state, the battery voltage (Vbat) is applied between thepositive and negative output terminals, and the braking threes on theright rear wheel electromagnetic brake 490 and the left rear wheelelectromagnetic brake 496 are thereby released. The diodes 464 b, 466 bare configured to absorb back surge from the right rear wheelelectromagnetic brake 490 and the left rear wheel electromagnetic brake496.

(Configuration of Shutoff Circuit 442)

As shown in FIG. 34 , the shutoff circuit 442 includes a switchingelement 442 a, a driver IC 442 b, and an AND gate 442 c. The switchingelement 442 a is for example a field effect transistor, and may morespecifically be a n-channel MOSFET having an insulated gate. A drain ofthe switching element 442 a is connected to the battery potential (Vbat)output of the control power supply circuit 432, a source of theswitching element 442 a is connected to the motor driver 462, and a gateof the switching element 442 a is connected to the driver IC 442 b. Afirst input terminal of the AND gate 442 c is connected to the switchcircuit 436, a second input terminal of the AND gate 442 c is connectedto the main MCU 434, and an output terminal of the AND gate 442 c isconnected to the driver IC 442 b. The driver IC 442 b is configured toelectrically conduct the switching element 442 a when the outputterminal of the AND gate 442 c has H potential, that is, when both thefirst input terminal and the second input terminal of the AND gate 442 chave H potential. The driver IC 442 b is configured not to electricallyconduct the switching element 442 a when the output terminal of the ANDgate 442 c has L potential, that is, when one of or both the first inputterminal and the second input terminal of the AND gate 442 c have Lpotential.

(configuration of Motor Driver 462)

The motor driver 462 is connected to the steering motor 176 via U-phase,V-phase, and W-phase output terminals. Further, the motor driver 462includes a first switching element 462 a, a second switching element 462b, a third switching element 462 c, a fourth switching element 462 d, afifth switching element 462 e, and a sixth switching element 462 f. Thefirst switching element 462 a, the second switching element 462 b, thethird switching element 462 c, the fourth switching element 462 d, thefifth switching element 462 e, and the sixth switching element 462 f mayfor example be field effect transistors, and may more specifically ben-channel MOSFETs with insulated gates.

A drain of the first switching element 462 a is connected to the sourceof the switching element 442 a in the shutoff circuit 442, a source ofthe first switching element 462 a is connected to the U-phase outputterminal, and a gate of the first switching element 462 a is connectedto the motor MCU 452. A drain of the second switching element 462 b isconnected to the U-phase output terminal, a source of the secondswitching element 462 b is connected to the ground potential, and a gateof the second switching element 462 b is connected to the motor MCU 452.

A drain of the third switching element 462 c is connected to the sourceof the switching element 442 a of the shutoff circuit 442, a source ofthe third switching element 462 c is connected to the V-phase outputterminal, and a gate of the third switching element 462 c is connectedto the motor MCU 452. A drain of the fourth switching element 462 d isconnected to the V-phase output terminal, a source of the fourthswitching element 462 d is connected to the ground potential, and a gateof the fourth switching element 462 d is connected to the motor MCU 452.

A drain of the fifth switching element 462 e is connected to the sourceof the switching element 442 a in the shutoff circuit 442, a source ofthe fifth switching element 462 e is connected to the W-phase outputterminal, and a gate of the fifth switching element 462 e is connectedto the motor MCU 452. A drain of the sixth switching element 462 f isconnected to the W-phase output terminal, a source of the sixthswitching element 462 f is connected to the ground potential, and a gateof the sixth switching element 462 f is connected to the motor MCD 452.

A detection signal of the Hall sensor 480 of the steering motor 176 isinputted to the motor MCU 452. The motor MCU 452 is configured tooperate the steering motor 176 at its desired rotation speed byswitching on/off of the first switching element 462 a, the secondswitching element 462 b, the third switching element 462 c, the fourthswitching element 462 d, the fifth switching element 462 e, and thesixth switching element 462 f in accordance with the detection signalfrom the Hall sensor 480. Further, the motor MCU 452 is configured toapply brake to rotation of the steering motor 176 with a so-called shortbrake by switching the second switching element 462 b, the fourthswitching element 462 d, and the sixth switching element 462 f to on.

(Processes Executed by Main MCD 434)

When the main power of the cart 2 shifts to the on-state, the main MCU434 executes processes shown in FIGS. 35 to 37 .

As shown in FIG. 35 , in S2, the main MCU 434 sets a temperatureprotection flag to 0.

In S4, the main MCU 434 determines whether an overload is detected inany of the overload detection sensors 320 a, 320 b, 320 c, 320 d. In acase where an overload is detected (if YES), the process proceeds to S6.In S6, the main MCU 434 sets an overload detection flag to 1. In a casewhere no overload is detected in S4 (if NO), the process proceeds to S8.In S8, the main MCD 434 sets the overload detection flag to 0. After 56or 58, the process proceeds to S10.

In S10, the main MCU 434 determines whether a collision is detected inany of the collision detection switches 530, 532. In a case where acollision is detected (if YES), the process proceeds to S12. In S12, themain MCU 434 sets a collision detection flag to 1. In a case where nocollision is detected in S10 (if NO), the process proceeds to S14. InS14, the main MCU 434 sets the collision detection flag to 0. After S12or S14, the process proceeds to S16.

In S16, the main MCU 434 determines whether any of brake circuittemperatures T detected in the thermistors 468 e, 470 e, 472 e, 474 eexceeds a temperature protection threshold T1. In a case where one ormore of the brake circuit temperatures T exceed the temperatureprotection threshold T1 (if YES), the process proceeds to S18. In S18,the main MCU 434 sets the temperature protection flag to 1. After S18,the process proceeds to S20. In a case where all of the brake circuittemperatures T do not exceed the temperature protection threshold T1 (ifNO) in S16, the process proceeds to S20.

In S20, the main MCU 434 determines whether the manual mode is selectedin the mode shifter switch 98. In a case where the manual mode isselected (if YES), the process proceeds to S34 (see FIG. 36 ). In a casewhere the manual mode is not selected (if NO), the process proceeds toS22.

In S22, the main MCU 434 determines whether the automatic mode isselected in the mode shifter switch 98. In a case where the automaticmode is selected (if YES), the process proceeds to S72 (see FIG. 37 ).In a case where the automatic mode is not selected (if NO), the processproceeds to S24.

The process of S24 is executed in a case where neither the manual modenor the automatic mode is selected in the mode shifter switch 98, thatis, in a case where the parking mode is selected in the mode shifterswitch 98. In S24, the main MCU 434 sets a target travelling speed V ofthe cart 2 to 0 km/h and sets a target turning angle θ of the cart 2 to0°. In S26, the main MCU 434 sends an electric conduction prohibitingsignal to the shutoff circuits 438, 440, 442.

In S28, the main MCU 434 calculates rotation speed command values forthe right front wheel motor 232, the left front wheel motor 242, theright rear wheel motor 486, and the left rear wheel motor 492 and asteering angle command value for the steering motor 176 from the targettravelling speed V and the target turning angle θ.

In S30, the main MCU 434 sends the rotation speed command values for theright front wheel motor 232, the left front wheel motor 242, the rightrear wheel motor 486, and the left rear wheel motor 492 and the steeringangle command value for the steering motor 176 to the motor MCUs 444,446, 448, 450, 452.

In S32, the main MCU 434 receives state signals from the motor MCUs 444,446, 448, 450, 452. After S32, the process returns to S2.

(Processes Executed by Main MCU 434 in Manual Mode)

The process of S34 shown in FIG. 36 is executed in the case where themanual mode is selected in the mode shifter switch 98. In S34, the mainMCU 434 determines whether the trigger switch 100 is operated to be theon-state based on an amount of the pressing operation on the triggerswitch 100 as inputted from the trigger switch 100. In a case where thetrigger switch 100 is operated to be in the on-state (if YES), theprocess proceeds to S36. In S36, the main MCU 434 sends an electricconduction permitting signal to the shutoff circuits 438, 440, 442.After S36, the process proceeds to S46.

In a case were the trigger switch 100 is not operated to be in theon-state (if NO) in S34, the process proceeds to S38. In S38, the mainMCU 434 sets the target travelling speed V of the cart 2 to 0 km/h, andsets the target turning angle θ of the cart 2 to 0°.

In S40, the main MCU 434 sends the electric conduction prohibitingsignal to the shutoff circuits 438, 440, 442.

In S42, the main MCU 434 determines whether all of the brake circuittemperatures T detected in the thermistors 468 e, 470 e, 472 e, 474 eare below a temperature protection-releasing threshold T2. In a casewhere of the brake circuit temperatures T are below the temperatureprotection-releasing threshold T2 (if YES), the process proceeds to S44.In a case where any of the brake circuit temperatures T is equal to orabove the temperature protection-releasing threshold T2 (if NO) in S42,the process proceeds to S28 (see FIG. 35 ).

The process of S44 is executed when the manual mode is selected in themode shifter switch 98, the target travelling speed V of the cart 2 isset to 0 km/h, the electric conduction prohibiting signal has been sentfrom the main MCU 434 to the shutoff circuits 438, 440, 442 (that is,the cart 2 is stopped), and all of the brake circuit temperatures T arebelow the temperature protection-releasing threshold T2. In S44, themain MCU 434 sets the temperature protection flag to 0. After S44, theprocess proceeds to S28 (see FIG. 35 ).

In S46, the main MCU 434 determines whether the forward motion isselected in the travelling direction shifter switch 102. In a case wherethe forward motion is selected (if YES), the process proceeds to S48.

In S48, the main MCU 434 determines whether the collision detection flagis 0. In a case where the collision detection flag is 0 (if YES), theprocess proceeds to S50.

In S50, the main MCU 434 determines whether the overload detection flagis 0. In a case where the collision detection flag is 0 (if YES), theprocess proceeds to S52.

In S52, the main MCU 434 determines whether the temperature protectionflag is 0. In a case where the temperature protection flag is 0 (ifYES), the process proceeds to S54.

In S54, the main MCU 434 sets the upper limit travelling speed of thecart 2 to a first upper limit travelling speed (such as 5 km/h). AfterS54, the process proceeds to S58.

In a case where the overload detection flag is 1 (if NO) in S50 and alsoin a case where the temperature protection flag is 1 (if NO) in S52, theprocess proceeds to S56. In S56, the main MCU 434 sets the upper limittravelling speed of the cart 2 to a second upper limit travelling speed(such as 1 km/h) that is lower than the first upper limit travellingspeed. After S56, the process proceeds to S58.

In S58, the main MCU 434 specifies the target travelling speed V of thecart 2 based on the amount of the pressing operation performed on thetrigger switch 100 as inputted from the trigger switch 100. In doing so,if the target travelling speed V specified based on the amount of thepressing operation performed on the trigger switch 100 is equal to orgreater than the upper limit travelling speed set in S54 or S56, themain MCU 434 adjusts the target travelling speed V to match the upperlimit travelling speed.

In S60, the main MCU 434 specifies the target turning angle θ of thecart 2 based on a rotation angle of the handle shaft 84 as inputted fromthe rotation angle sensor 88. After S60, the process proceeds to S28(see FIG. 35 ).

In a case where the collision detection flag is 1 (if NO) in S48, theprocess proceeds to S62. The process of S62 is executed when the manualmode is selected in the mode shifter switch 98, the forward motion isselected in the travelling direction shifter switch 102, and thecollision detection flag is 1. In S62, the main MCU 434 sets the targettravelling speed V of the cart 2 to 0 km/h and sets the target turningangle θ of the cart 2 to 0°. In S64, the main MCU 434 sends the electricconduction prohibiting signal to the shutoff circuits 438, 440, 442.After S64, the process proceeds to S28 (see FIG. 35 ).

In a case where the backward motion is selected in the travellingdirection shifter switch 102 (if NO) in S46, the process proceeds toS66. The process of S66 is executed when the manual mode is selected inthe mode shifter switch 98 and the backward motion is selected in thetravelling direction shifter switch 102. In S66, the main MCU 434 setsthe upper limit travelling speed of the cart 2 to the second upper limittravelling speed (such as 1 km/h).

In S68, the main MCU 434 specifies the target travelling speed V of thecart 2 based on the amount of the pressing operation performed on thetrigger switch 100 as inputted from the trigger switch 100. In doing so,if the target travelling speed V specified based on the amount of thepressing operation performed on the trigger switch 100 is equal to orgreater than the upper limit travelling speed set in S66, the main MCU434 adjusts the target travelling speed V to match the upper limittravelling speed.

In S70, the main MCU 434 specifies the target turning angle θ of thecart 2 based on the rotation angle of the handle shaft 84 as inputtedfrom the rotation angle sensor 88. After S70, the process proceeds toS28 (see FIG. 35 ).

The upper limit travelling speed of the cart 2 in the process of S54 maysuitably be changed in accordance with an operation that was performedon the speed shifter switch 104. For example, when the travelling speedof the cart 2 is set to high speed in the speed shifter switch 104, theupper limit travelling speed of the cart 2 may be set to the first upperlimit travelling speed (such as 5 km/h); when the travelling speed ofthe cart 2 is set to medium speed in the speed shifter switch 104, theupper limit travelling speed of the cart 2 may be set to a third upperlimit travelling speed (such as 3 km/h) that is lower than the firstupper limit travelling speed and higher than the second upper limittravelling speed; and when the travelling speed of the cart 2 is set tolow speed in the speed shifter switch 104, the upper limit travellingspeed of the cart 2 may be set to a fourth upper limit travelling speed(such as 1.5 km/h) that is lower than the third upper limit travellingspeed and higher than the second upper limit travelling speed.

(Processes Executed by MCU 434 in Automatic Mode)

The process of S72 shown in FIG. 37 is executed when the automatic modeis selected in the mode shifter switch 98. In S72, the main MCU 434determines whether the collision detection flag is 0. In a case wherethe collision detection flag is 0 (if YES), the process proceeds to S74.

In S74, the main MCU 434 determines whether the overload detection flagis 0. In a case where the overload detection flag is 0 (if YES), theprocess proceeds to S76.

In S76, the main MCU 434 sends the electric conduction permitting signalto the shutoff circuits 438, 440, 442.

In S78, the main MCU 434 determines whether the temperature protectionflag is 0. In a case where the temperature protection flag is 0 (ifYES), the process proceeds to S80. In S80, the main MCU 434 sets theupper limit travelling speed of the cart 2 to the third upper limittravelling speed (such as 3 km/h). After S80, the process proceeds toS84.

In a case where the temperature protection flag is 1 (if NO) in S78, theprocess proceeds to S82. In S82, the main MCU 434 sets the upper limittravelling speed of the cart 2 to the second travelling speed (such as 1km/h). After S82, the process proceeds to S84.

In S84, the main MCU 434 specifies the target travelling speed V of thecart 2 based on the command value from the automatic driving MCU 430. Indoing so, if the target travelling speed V specified based on thecommand value from the automatic driving MCU 430 is equal to or higherthan the upper limit travelling speed set in S80 or S82, the main MCU434 adjusts the target travelling speed V to match the upper limittravelling speed.

In S86, the main MCU 434 specifies the target turning angle θ of thecart 2 based on the command value from the automatic driving MCU 430.After S86, the process proceeds to S28 (see FIG. 35 ).

In a case where the collision detection flag is 1 (if NO) in S72, andalso in a case where the overload detection flag is 1 if NO) in S74, theprocess proceeds to S88. The process of S88 is executed when theautomatic mode is selected in the mode shifter switch 98 and thecollision detection flag is 1, or when the automatic mode is selected inthe mode shifter switch 98 and the overload detection flag is 1. In S88,the main MCU 434 sets the target travelling speed V of the cart 2 to 0km/h and sets the target turning angle θ of the cart 2 to 0°. In S90,the main MCU 434 sends the electric conduction prohibiting signal to theshutoff circuits 438, 440, 442. After S90, the process proceeds to S28(see FIG. 35 ).

(Processes Executed by Motor MCUs 444, 446)

When the main power of the cart 2 shifts to the on-state, each of themotor MCUs 444, 446 executes the processes shown in FIGS. 38 and 39 .

As shown in FIG. 38 , in S102, the motor MCUs 444, 446 receive a commandsignal from the main MCU 434.

In S104, the motor MCUs 444, 446 specify target rotation speeds RS1 ofthe right front wheel motor 232 and the left front wheel motor 242 basedon the command signal received from the main MCU 434.

In S106, the motor MCUs 444, 446 specify current rotation speeds RS2 ofthe right front wheel motor 232 and the left front wheel motor 242 basedon the detection signals received from the Hall sensors 482, 484.

In S108, the motor MCUs 444, 446 each determine whether the targetrotation speed RS1 specified in S104 is higher than the current rotationspeed RS2 specified in S106. In a case where the target rotation speedRS1 is higher than the current rotation speed RS2 (if YES), the processproceeds to S110.

In S110, the motor MCUs 444, 446 execute PWM control on the right frontwheel motor 232 and the left front wheel motor 242 using the motordrivers 454, 456 to accelerate rotation of the right front wheel motor232 and the left front wheel motor 242. In this S110, the motor MCUs444, 446 input 0 as current command values to the brake circuits 468,470 and thereby disable operations of the brake circuits 468, 470.

In S112, the motor MCUs 444, 446 each specify target rotationacceleration RA1 based on a difference between the target rotation speedRS1 specified in S104 and the current rotation speed RS2 specified inS106.

In S114, the motor MCUs 444, 446 each specify current rotationacceleration RA2 based on the detection signal received from thecorresponding Hall sensor 482, 484.

In S116, the motor MCUs 444, 446 each determine whether the targetrotation acceleration RA1 specified in S112 is greater than the currentrotation acceleration RA2 specified in S114. In a case where the targetrotation acceleration RA1 is greater than the current rotationacceleration RA2 (if YES), the process proceeds to S118. In S118, themotor MCUs 444, 446 increase duty ratios in the PWM control of the rightfront wheel motor 232 and the left front wheel motor 242 by the motordrivers 454, 456. In a case where the target rotation acceleration RA1is equal to or smaller than the current rotation acceleration RA2 (ifNO) in S116, the process proceeds to S120. In S120, the motor MCUs 444,446 decrease the duty ratios in the PWM control of the right front wheelmotor 232 and the left front wheel motor 242 by the motor drivers 454,456. After S118 or S120, the process proceeds to S134 (see FIG. 39 ).

In a case where the target rotation speed RS1 is equal to or smallerthan the current rotation speed RS2 (if NO) in S108, the processproceeds to S122. In S122, the motor MCUs 444, 446 decelerate therotation of the right front wheel motor 232 and the left front wheelmotor 242 using the brake circuits 468, 470. In this S122, the motorMCUs 444, 446 disable operations of the motor drivers 454, 456.

In S124, the motor MCUs 444, 446 each specify a target rotationdeceleration RD1 based on a difference between the target rotation speedRS1 specified in S104 and the current rotation speed RS2 specified inS106.

In S126, the motor MCUs 444, 446 each specify a current rotationdeceleration RD2 based on the detection signal received from thecorresponding Hall sensor 482, 484.

In S128, the motor MCUs 444, 446 each determine whether the targetrotation deceleration RD1 specified in S124 is smaller than the currentrotation deceleration RD2 specified in S126. In a case where the targetrotation deceleration RD1 is smaller than the current rotationdeceleration RD2 (if YES), the process proceeds to S130. In S130, themotor MCUs 444, 446 increase the current command values to the brakecircuits 468, 470. In a case where the target rotation deceleration RD1is equal to or greater than the current rotation deceleration RD2 (ifNO) in S128, the process proceeds to S132. In S132, the motor MCUs 444,446 decrease the current command values to the brake circuits 468, 470.After S130 or S132, the process proceeds to S134 (see FIG. 39 ).

As shown in FIG. 39 , in S134, the motor MCUs 444, 446 each determinewhether the brake circuit temperature T detected in the correspondingthermistor 468 e, 470 e exceeds a cooling-start temperature T3. In acase where the brake circuit temperature T exceeds the cooling-starttemperature T3 (if YES), the process proceeds to S136. In S136, themotor MCUs 444, 446 actuate the cooling fans 50 d, 52 d and cool theelectrical brake circuit boards 50, 52. After S136, the process proceedsto S138. In a case where the brake circuit temperature T is equal to orlower than the cooling-start temperature T3 (if NO) in S134, the processproceeds to S138.

In S138, the motor MCUs 444, 446 each determine whether the brakecircuit temperature T detected in the corresponding thermistor 468 e,470 e is below a cooling-end temperature T4 that is lower than thecooling-start temperature T3. In a case where the brake circuittemperature T is below the cooling-end temperature T4 (if YES), theprocess proceeds to S140. In S140, the motor MCUs 444, 446 stop thecooling fans 50 d, 52 d and end to cool the electrical brake circuitboards 50, 52. After S140, the process proceeds to S142. In a case wherethe brake circuit temperature T is equal to or higher than thecooling-end temperature T4 (if NO) in S138, the process proceeds toS142.

In S142, the motor MCUs 444, 446 send the state signals to the main MCU434. After S142, the process returns to S102 (see FIG. 38 ).

As above, the motor MCUs 444, 446 are configured to actuate the coolingfans 50 d, 52 d based on the brake circuit temperatures T detected bythe thermistors 468 e, 470 e and thereby cool the electrical brakecircuit boards 50, 52. By configuring as such, the motor 444, 446 cancontinuously brake the front wheel motor 232 and the left front wheelmotor 242 using the brake circuits 468, 470 over a long period of time.For example, the motor MCUs 444, 446 can continue the braking operationon the right front wheel motor 232 and the left front wheel motor 242 bythe brake circuits 468, 470 for more than 15 minutes, specifically formore than 30 minutes, and more specifically, for more than an hour.

(Processes Executed by Motor MCUs 448, 450)

When the main power of the cart 2 shifts to the on-state, the motor MCUs448, 450 execute processes shown in FIGS. 40 and 41 .

As shown in FIG. 40 , in S152, the motor MCUs 448, 450 receive thecommand signal from the main MCU 434.

In S154, the motor MCUs 448, 450 specify target rotation speeds RS1 ofthe right rear wheel motor 486 and the left rear motor 492 based on thecommand signal received from the main MCU 434.

In S156, the motor MCUs 448, 450 specify current rotation speeds RS2 ofthe right rear wheel motor 486 and the left rear wheel motor 492 basedon the detection signals received from the Hall sensors 488, 494.

In S158, the motor MCUs 448, 450 each determine whether the targetrotation speed RS1 specified in S154 is equal to or higher than a lowerlimit rotation speed RS0. In a case where the target rotation speed RS1is equal to or higher than the lower limit rotation speed RS0 (if YES),the process proceeds to S160. In S160, the motor MCUs 448, 450 turn offthe right rear wheel electromagnetic brake 490 and the left rear wheelelectromagnetic brake 496 using the electromagnetic brake drivers 464,466. After S160 the process proceeds to S162. In a case where the targetrotation speed RS1 is below the lower limit rotation speed RS0 (if NO),the so process proceeds to S162.

In S162, the motor MCUs 448, 450 each determine whether the currentrotation speed RS2 specified in S156 is equal to or lower than the lowerlimit rotation speed RS0. In a case where the current rotation speed RS2is equal to or lower than the lower limit rotation speed RS0 (if YES),the process proceeds to S164. In S164, the motor MCUs 448, 450 turn onthe right rear wheel electromagnetic brake 490 and the left rear wheelelectromagnetic brake 496 using the electromagnetic brake drivers 464,466. After S164, the process proceeds to S192 (see FIG. 41 ). In a casewhere the current rotation speed RS2 exceeds the lower limit rotationspeed RS0 (if NO), the process proceeds to S166.

In S166, the motor MCUs 448, 450 each determine whether the targetrotation speed RS1 specified in S154 is higher than the current rotationspeed RS2 specified in S156. In a case where the target rotation speedRS1 is higher than the current rotation speed RS2 (if YES), the processproceeds to S168.

In S168, the motor MCUs 448, 450 accelerate the rotation of the rightrear wheel motor 486 and the left rear wheel motor 492 by executing PWMcontrol on the right rear wheel motor 486 and the left rear wheel motor492 using the motor drivers 458, 460. In S168, the motor MCUs 448, 450input 0 as the current command values to the brake circuits 472, 474 andthereby disable operations of the brake circuits 472, 474.

In S170, the motor MCUs 448, 450 each specify the target rotationacceleration RA1 based on a difference between the target rotation speedRS1 specified in S154 and the current rotation speed RS2 specified inS156.

In S172, the motor MCUs 448, 450 each specify the current rotationacceleration RA2 based on the detection signal received from thecorresponding Hall sensor 488, 494.

In S174, the motor MCUs 448, 450 each determine whether the targetrotation acceleration RA1 specified in S170 is greater than the currentrotation acceleration RA2 specified in S172. In a case where the targetrotation acceleration RA1 is greater than the current rotationacceleration RA2 (if YES), the process proceeds to S176. In S176, themotor MCUs 448, 450 increase duty ratios in the PWM control of the rightrear wheel motor 486 and the left rear wheel motor 492 by the motordrivers 458, 460. In a case where the target rotation acceleration RA1is equal to or smaller than the current rotation acceleration RA2 (ifNO) in S174, the process proceeds to S178. In S178, the motor MCUs 448,450 decrease the duty ratios in the PWM control of the right rear wheelmotor 486 and the left rear wheel motor 492 by the motor drivers 458,460. After S176 or S178, the process proceeds to S192 (see FIG. 41 ).

In a case where the target rotation speed RS1 is equal to or smallerthan the current rotation speed RS2 (if NO) in S166, the processproceeds to S180. In S180, the motor MCUs 448, 450 decelerate therotation of the right rear wheel motor 486 and the left rear wheel motor492 using the brake circuits 472, 474. In this S180, the motor MCUs 448,450 disable operations of the motor drivers 458, 460.

In S182, the motor MCUs 448, 450 each specify the target rotationdeceleration RD1 based on a difference between the target rotation speedRS1 specified in S154 and the current rotation speed RS2 specified inS156.

In S184 the motor MCUs 448, 450 each specify the current rotationdeceleration RD2 based on the detection signal received from thecorresponding Hall sensor 488, 494.

In S186, the motor MCUs 448, 450 each determine whether the targetrotation deceleration RD1 specified in S182 is smaller than the currentrotation deceleration RD2 specified in S184. In a case where the targetrotation deceleration RD1 is smaller than the current rotationdeceleration RD2 (if YES), the process proceeds to S188. In S188, themotor MCUs 448, 450 increase the current command values to the brakecircuits 472, 474. In a case where the target rotation deceleration RD1is equal to or greater than the current rotation deceleration RD2 (ifNO) in S186, the process proceeds to S190. In S190, the motor MCUs 448,450 decrease the current command values to the brake circuits 472, 474.After S188 or S190, the process proceeds to S192 (see FIG. 41 ).

As shown in FIG. 41 , in S192, the motor MCUs 448, 450 each determinewhether the brake circuit temperature T detected in the correspondingthermistor 472 e, 474 e exceeds the cooling-start temperature T3. In acase where the brake circuit temperature T exceeds the cooling-starttemperature T3 (if YES), the process proceeds to S194. In S194, themotor MCUs 448, 450 actuate the cooling fans 54 d, 56 d and cool theelectrical brake circuit boards 54, 56. After S194, the process proceedsto S196. In case where the brake circuit temperature T is equal to orlower than the cooling-start temperature T3 (if NO) in S192, the processproceeds to S196.

In S196, the motor MCUs 448, 450 each determine whether the brakecircuit temperature T detected in the corresponding thermistor 472 e,472 e is below the cooling-end temperature T4. In a case where the brakecircuit temperature T is below the cooling-end temperature T4 (if YES),the process proceeds to S198. In S198, the motor MCUs 448, 450 stop thecooling fans 54 d, 56 d and end to cool the electrical brake circuitboards 54, 56. After S198, the process proceeds to S200. In a case wherethe brake circuit temperature T is equal to or higher than thecooling-end temperature T4 (if NO) in S196, the process proceeds toS200.

In S200, the motor MCUs 448, 450 send the state signals to the main MCU434. After S200, the process returns to S152 (see FIG. 40 ).

FIG. 42 shows an example of changes in the travelling speed, the brakecurrent, and the brake circuit temperature over time, in a case wherethe cart 2 travels on flatland and downhill in the manual mode. In theexample shown in FIG. 42 , the manual mode is selected in the modeshifter switch 98, and the forward motion is selected in a forwardmotion/backward motion shifter switch. When the trigger switch 100 isswitched from off to on at time t1, the right rear wheel electromagneticbrake 490 and the left rear electromagnetic brake 496 are released bythe electromagnetic brake drivers 464, 466, and the cart 2 starts tomove forward by the motor drivers 454, 456, 458, 460 driving the rightfront wheel motor 232, the left front wheel motor 242, the right rearwheel motor 486, and the left rear wheel motor 492. When the travellingspeed of the cart 2 reaches the first upper limit travelling speed attime t2, the brake circuits 468, 470, 472, 474 are actuated andelectrical brake is applied to the right front wheel motor 232, the leftfront wheel motor 242, the right rear wheel motor 486, and the left rearwheel motor 492. Since the brake circuits 468, 470, 472, 474 remainactuated even after the cart 2 moved from the flatland to the downhill,the travelling speed of the cart 2 is maintained at the first upperlimit travelling speed. Further, as the brake circuits 468, 470, 472,474 continue to operate, the temperatures of the brake circuits 468,470, 472, 474 increase. When the temperatures of the brake circuits 468,470, 472, 474 exceed the temperature protection threshold T1 at time t3,the upper limit travelling speed of the cart 2 switches from the firstupper limit travelling speed to the second upper limit travelling speed,and the brake circuits 468, 470, 472, 474 apply stronger electricalbrake on the right front wheel motor 232, the left front wheel motor242, the right rear wheel motor 486, and the left rear wheel motor 492.Due to this, the travelling speed of the cart 2 decreases, however, thetemperatures of the brake circuits 468, 470, 472, 474 increase at afaster rate. When the travelling speed of the cart 2 decreases to thesecond upper limit travelling speed at time t4, the electrical brakewhich the brake circuits 468, 470, 472, 474 apply to the right frontwheel motor 232, the left front wheel motor 242, the right rear wheelmotor 486, and the left rear wheel motor 492 becomes weaker, by whichthe temperatures of the brake circuits 468, 470, 472, 474 drop. Thistemperature protection is not released until the cart 2 stops even afterthe temperatures of the brake circuits 468, 470, 472, 474 drop below thetemperature protection threshold T1 and further drop below thetemperature protection-releasing threshold T2, so the upper limittravelling speed of the cart 2 is maintained at the second upper limittravelling speed. When the trigger switch 100 is switched from on to offat time t5, strong electrical brake, is applied to the right front wheelmotor 232, the left front wheel motor 242, the right rear wheel motor486, and the left rear wheel motor 492 by the brake circuits 468, 470,472, 474. When the cart 2 stops at time in, the temperature protectionis released, and the upper limit travelling speed of the cart 2 switchesfrom the second upper limit travelling speed to the first upper limittravelling speed. Further, when the cart 2 stops at time t6, theelectrical brake by the brake circuits 468, 470, 472, 474 is terminatedand short brake by the motor drivers 454, 456, 458, 460 is applied tothe right front wheel motor 232, the left front wheel motor 242, theright rear wheel motor 486, and the left rear wheel motor 492, andthereafter the right rear wheel 252 and the left rear wheel 272 arelocked by the right rear wheel electromagnetic brake 490 and the leftrear wheel electromagnetic, brake 496. After the electrical brake by thebrake circuits 468, 470, 472, 474 is terminated, the temperatures of thebrake circuits 468, 470, 472, 474 continue to drop. After this, when thetrigger switch 100 is switched again from off to on at time t7, theright rear wheel electromagnetic brake 490 and the left rear wheelelectromagnetic brake 496 are released by the electromagnetic brakedrivers 464, 466, and the cart starts to move forward by the motordrivers 454, 456, 458, 460 driving the right front wheel motor 232, theleft front wheel motor 242, the right rear wheel motor 486, and the leftrear wheel motor 492. When the travelling speed of the cart 2 reachesthe first upper limit travelling speed at time t8, the brake circuits468, 470, 472, 474 are actuated and electrical brake is applied to theright front wheel motor 232, the left front wheel motor 242, the rightrear wheel motor 486, and the left rear wheel motor 492.

(Processes Executed by Motor MCU 452)

When the main power of the cart 2 shifts to the on-state, the motor MCU452 executes processes shown in FIG. 43 .

In S202, the motor MCU 452 receives a command signal from the main MCU434.

In S204, the motor MCU 452 specifies a target steering angle δ of thesteering unit 10 based on the command signal received from the main MCU434.

In S206, the motor MCU 452 specifies a current steering angle γ of thesteering unit 10 based on the detection signal received from thesteering angle sensor 166.

In S208, the motor MCU 452 determines whether the target steering angleδ specified in S204 matches the current steering angle γ specified inS206. In a case where the target steering angle δ does not match thecurrent steering angle γ (if NO), the process proceeds to S210.

In S210, the motor MCU 452 specifies a target rotation speed PR1 of thesteering motor 176 based on a difference between the target steeringangle δ specified in S204 and the current steering angle γ specified inS206.

In S212, the motor MCU 452 drives the steering motor 176 by PWM controlusing the motor driver 462 so that the steering motor 176 rotates at thetarget rotation speed PR1 specified in S210. After S212, the processproceeds to S216.

In a case where the target steering angle δ matches the current steeringangle γ (if YES) in S208, the process proceeds to S214. In S214, themotor MCU 452 applies short brake on the steering motor 176 using themotor driver 462. After S214, the process proceeds to S216.

In S216, the motor MCU 452 sends the state signal to the main MCU 434.After S216, the process returns to S202.

(Variants)

In the above embodiment, the right front wheel motor 232, the left frontwheel motor 242, the right rear wheel motor 486, and the left rear wheelmotor 492 may be in-wheel motors (not shown) that are respectivelyincorporated in the right front wheel 192, the left front wheel 212, theright rear wheel 252, and the left rear wheel 272.

In the above embodiment, the steering motor 176, the front wheel motor232, the left front wheel motor 242, the right rear wheel motor 486, andthe left rear wheel motor 492 may be outer rotor brushless DC motors,may be brushed DC motors, may be AC motors or may be other types ofmotors.

In the above embodiment, the motor MCUs 444, 446, 448, 452 may detectthe rotation speeds of the right front wheel motor 232, the left frontwheel motor 242, the right rear wheel motor 486, the left rear wheelmotor 492, and the steering motor 176 by using circuits configured todetect inductive voltages in the right front wheel motor 232, the leftfront wheel motor 242, the right rear wheel motor 486, the left rearwheel motor 492, and the steering motor 176 instead of the Hall sensors482, 484, 488, 494, 480.

In the above embodiment, the cart 2 may be configured to move by usingcontinuous track units (crawler units) each including driving wheel(s)and driven wheel(s) arranged along a front-rear direction, a beltstrapped on the driving wheel(s) and the driven wheel(s), and motor(s)for rotating the driving wheel(s) instead of the front wheel unit 12 andthe rear wheel unit 14.

In the above embodiment, the steering unit 10 may cause the steeringshaft 168 to pivot using a different type of actuator rather than thesteering motor 176.

In the above embodiment, the bumper unit 16 is arranged at a frontportion of the cart 2, and the collision detection switches 530, 532thereby detect frontal collision to the cart 2. Unlike thisconfiguration, the bumper unit 16 may be arranged at a rear portion ofthe cart 2, and the collision detection switches 530, 532 may therebydetect rear-end collision to the cart 2. Alternatively, two bumper units16 may be arranged at the front and rear portions of the cart 2, and thecollision detection switches 530, 532 in each of the bumper units 16 maydetect their corresponding one of the frontal or rear-end collisions tothe cart 2. In a case where the bumper unit 16 is arranged at a rearportion of the cart 2 and the collision detection switches 530, 532 areto detect the rear-end collision to the cart 2, the processes executedin connection thereto may proceed to S50 in a case where the forwardmotion is selected (if YES) in S46 of FIG. 36 , may proceed to S48 in acase where the backward motion is selected (if NO) in S46 may proceed toS66 in a case where the collision detection flag is 0 (if YES) in S48,and may proceed to S62 in a case where the collision detection flag is 1(if NO) in S48.

In the above embodiment, the handle unit 8 may include a cover member(not shown) configured to cover the movable cam member 90, the fixed cammember 92, the coil spring 94, and a part of the handle shaft 84. Inthis case, the fixing member 82 may constitute a part of the covermember.

In the above embodiment, the handle unit 8 may include another type ofelastic member instead of the coil spring 94. Further, the handle unit 8may include a damper (not shown) configured to apply a damping force topivoting of the handle shaft 84.

In the above embodiment, the case in which the overload detectionsensors 320 a, 320 b, 320 c, 320 d, 380 are photo interrupters has beenexplained however, the overload detection sensors 320 a, 320 b, 320 c,320 d, 380 may be photo reflectors configured to detect presence/absenceof light reflection by the detection portions 348 a, 348 b, 348 c, 348d, 416, may be magnetic sensors configured to detect magnetism ofmagnets arranged in the detection portions 348 a, 348 b, 348 c, 348 d,416, or may be other types of known contactless detection sensors.Alternatively, the overload detection sensors 320 a, 320 b, 320 c, 320d, 380 may be contact detection sensors.

In the above embodiment, the case in which the switching elements 468 a,470 a, 472 a, 474 a of the brake circuits 468, 470, 472, 474 aren-channel MOSFETS has been explained, however, the switching elements468 a, 470 a, 472 a, 474 a may be p-channel MOSFETs, IGBTs, bipolartransistors, or other types of transistors. Alternatively, the switchingelements 468 a, 470 a, 472 a, 474 a may be other types of electronicallyvariable resistance elements such as thyristors. The switching elements468 a, 470 a, 472 a, 474 a may be constituted of Si semiconductors, SiCsemiconductors, GaN semiconductors, or other types of semiconductors.

As above, in one or more embodiments, the cart 2 comprises: the rightfront wheel 192 (or the left front wheel 212, the right rear wheel 252,or the left rear wheel 272) (examples of driving wheel); the right frontwheel motor 232 (or the left front wheel motor 242, the right rear wheelmotor 486, or the left rear wheel motor 492) (examples of motor)configured to rotate the right front wheel 192 (or the left front wheel212, the right rear wheel 252, or the left rear wheel 272); the motordriver 454 (or the motor driver 456, 458, or 460) (examples of motordrive circuit) configured to drive the right front wheel motor 232 (orthe left front wheel motor 242, the right rear wheel motor 486, or theleft rear wheel motor 492); the brake circuit 468 (or the brake circuit470, 472, or 474) (examples of motor brake circuit) configured toelectrically brake the right front wheel motor 232 (or the left frontwheel motor 242, the right rear wheel motor 486, or the left rear wheelmotor 492); the main MCU 434 and the motor MCU 444, 446, 448, or 450(examples of control device) configured to control the right front wheelmotor 232 (or the left front wheel motor 242, the right rear wheel motor486, or the left rear wheel motor 492) via the motor driver 454 (or themotor driver 456, 458, or 460) and the brake circuit 468 (or the brakecircuit 470, 472, or 474) so that the travelling speed of the cart 2becomes equal to or lower than the upper limit travelling speed; and thethermistor 468 e (or the thermistor 470 e, 472 e, or 474 e) (examples oftemperature sensor) configured to detect the temperatures of the brakecircuit 468 (or the brake circuit 470, 472, or 474). When the upperlimit travelling speed is the first upper limit travelling speed (suchas 5 km/h) and the temperature detected by the thermistor 468 e (or thethermistor 470 e, 472 e, or 474 e) exceeds the temperature protectionthreshold T1 (an example of predetermined temperature), the main MCU 434is configured to change the upper limit travelling speed to the secondupper limit travelling speed (such as 1 km/h) lower than the first upperlimit travelling speed.

When the travelling speed of the cart 2 becomes high, the generated heatquantity in the brake circuit 468 (or the brake circuit 470, 472, or474) for braking the right front wheel motor 232 (or the left frontwheel motor 242, the right rear wheel motor 486, and the left rear wheelmotor 492) increases, h which the brake circuit 468 (or the brakecircuit 470, 472, or 474) comes to have an accordingly highertemperature. According to the above configuration, the generated heatquantity in the brake circuit 468 (or the brake circuit 470, 472, or474) for braking the right front wheel motor 232 (or the left frontwheel motor 242, the right rear wheel motor 486, or the left rear wheelmotor 492) can be reduced by reducing the upper limit travelling speedof the cart 2 from the first upper limit traveling speed to the secondupper limit travelling speed when the temperature of the brake circuit468 (or the brake circuit 470, 472, or 474) detected by the thermistor468 e (or thermistor 470 e, 472 e, 474 e) exceeds the temperatureprotection threshold T1. The brake circuit 468 (or the brake circuit470, 472, or 474) can be suppressed from reaching a high temperature.

In one or more embodiments, when the temperature detected by thethermistor 468 e (or the thermistor 470 e, 472 e, or 474 e) becomeslower than the temperature protection-releasing threshold T2 (an exampleof second predetermined temperature) lower than the temperatureprotection threshold T1 after the upper limit travelling speed has beenchanged from the first upper limit travelling speed to the second upperlimit travelling speed, the main MCU 434 is configured to set the upperlimit travelling speed back to the first upper limit travelling speed.

According to the above configuration, after the brake circuit 468 (orthe brake circuit 470, 472, or 474) reaches a high temperature and theupper limit travelling speed is thus reduced, the upper limit travellingspeed is not set back to its original speed until the brake circuit 468(or the brake circuit 470, 472, or 474) is sufficiently cooled, thus theupper limit travelling speed can be suppressed from frequently beingincreased and reduced.

In one or more embodiments, the cart 2 further comprises the triggerswitch 100 (an example of operation member) for receiving an operationby the user. The cart 2 is configured to operate in the manual mode andthe automatic mode, wherein in the manual mode, the right front wheelmotor 232 (or the left front wheel motor 242, the right rear wheel motor486, the left rear wheel motor 492) is driven when the trigger switch100 is on, and the right front wheel motor 232 (or the left front wheelmotor 242, the right rear wheel motor 486, the left rear wheel motor492) is stopped when the trigger switch 100 is off, and in the automaticmode, the right front wheel motor 232 (or the left front wheel motor242, the right rear wheel motor 486, the left rear wheel motor 492) isdriven regardless of whether the trigger switch 100 is on or off. Evenwhen the temperature detected by the thermistor 468 e (or thethermistors 470 e, 472 e, 474 e) becomes lower than the temperatureprotection-releasing threshold T2 after the upper limit travelling speedis changed from the first upper limit travelling speed to the secondlimit travelling speed, the main MCU 434 is configured not to set theupper limit travelling speed back to the first upper limit travellingspeed if the operation mode of the cart 2 is the automatic mode.

If the cart 2 is operating in the automatic mode when the brake circuit468 (or the brake circuit 470, 472, or 474) is cooled sufficiently andthe upper limit travelling speed is to be set back to the first upperlimit travelling speed from the second upper limit travelling speed,there is a risk that the cart 2 suddenly accelerates. According to theabove configuration, after the brake circuit 468 (or the brake circuit470, 472, or 474) reaches a high temperature and the upper limittravelling speed is thus reduced, the upper limit travelling speed isnot set back to its original speed even if the brake circuit 468 (or thebrake circuit 470, 472, or 474) is cooled sufficiently if the operationmode of the cart 2 is the automatic mode. Thus, the cart 2 can besuppressed from suddenly accelerating.

In one or more embodiments, even when the temperature detected by thethermistor 468 e (or the thermistor 470 e, 472 e, or 474 e) becomeslower than the temperature protection-releasing threshold T2 and theoperation mode of the cart 2 is not the automatic mode after the upperlimit travelling speed has been changed from the first upper limittravelling speed to the second upper limit travelling speed, the mainMCU 434 is configured not to set the upper limit travelling speed backto the first upper limit travelling speed if the cart 2 is not stopped.

Even when the brake circuit 468 (or the brake circuit 470, 472, or 474)is cooled sufficiently and the operation mode of the cart 2 is not theautomatic mode, there is a risk that the cart 2 suddenly accelerates ifthe cart 2 is not stopped upon setting the upper limit travelling speedback to the first upper limit travelling speed from the second upperlimit travelling speed. According to the above configuration, after thebrake circuit 468 (or the brake circuit 470, 472, or 474) reaches a hightemperature and the upper limit travelling speed is thus reduced, theupper limit travelling speed is not set back to its original speed untilthe cart 2 is stopped, even when the motor brake circuit 468 (or thebrake circuit 470, 472, or 474) is cooled sufficiently and the operationmode of the cart 2 is not the automatic mode. Thus, the cart 2 can besuppressed from suddenly accelerating.

In one or more embodiments, even when the temperature detected by thethermistor 468 e (or the thermistor 470 e, 472 e, or 474 e) becomeslower than the temperature protection-releasing threshold T2 after theupper limit travelling speed has been changed from the first upper limittravelling speed to the second upper limit travelling speed, the mainMCU 434 is configured not to set the upper limit travelling speed backto the first upper limit travelling speed if the cart 2 is not stopped.

When the brake circuit 468 (or the brake circuit 470, 472, or 474) iscooled sufficiently and the upper limit travelling speed is to be setback to the first upper limit travelling speed from the second upperlimit travelling speed, there is a risk that the 2 cart suddenlyaccelerates if the cart 2 is not stopped. According to the aboveconfiguration, after the brake circuit 468 (or the brake circuit 470,472, or 474) reaches a high temperature and the upper limit travellingspeed is thus reduced, the upper limit travelling speed is not set backto its original speed until the cart 2 is stopped even if the brakecircuit 468 (or the brake circuit 470, 472, or 474) is cooledsufficiently. Thus, the cart 2 can be suppressed from suddenlyaccelerating.

In one or more embodiments, the cart 2 further comprises the triggerswitch 100 (an example of operation member) for receiving an operationby the user. The cart 2 is configured to operate in the manual mode andthe automatic mode. In the manual mode, the right front wheel motor 232(or the left front wheel motor 242, the right rear wheel motor 486, theleft rear wheel motor 492) is driven when the trigger switch 100 is on,and the right front wheel motor 232 (or the left front wheel motor 242,the right rear wheel motor 486, the left rear wheel motor 492) isstopped when the trigger switch 100 is off. In the automatic mode, theright front wheel motor 232 for the left front wheel motor 242, theright rear wheel motor 486, the left rear wheel motor 492) is drivenregardless of whether the trigger switch 100 is on or off. After theupper limit travelling speed has been changed from the first upper limittravelling speed to the second upper limit travelling speed, the mainMCU 434 is configured to set the upper limit travelling speed back tothe first upper limit travelling speed if the operation mode of the cart2 is not the automatic mode.

When the upper limit travelling speed is to be set back to the firstupper limit travelling speed from the second upper limit travellingspeed, there is a risk that the cart 2 suddenly accelerates if the cart2 is operating in the automatic mode. According to the aboveconfiguration, after the brake circuit 468 (or the brake circuit 470,472, or 474) reaches a high temperature and the upper limit travellingspeed is thus reduced, the upper limit travelling speed is not set backto its original speed if the operation mode of the cart 2 is theautomatic mode. Thus, the cart 2 can be suppressed from suddenlyaccelerating.

In one or more embodiments, even when the operation mode of the cart 2is not the automatic mode after the upper limit travelling speed hasbeen changed from the first upper limit travelling speed to the secondupper limit travelling speed, the main MCU 434 is configured not to setthe upper limit travelling speed back to the first upper limittravelling speed if the cart 2 is not stopped.

Even when the operation mode of the cart 2 is not the automatic mode, ifthe cart 2 is not stopped upon setting the upper limit travelling speedback to the first upper limit travelling speed from the second upperlimit travelling speed, there is a risk that the cart 2 suddenlyaccelerates. According to the above configuration, after the brakecircuit 468 (or the brake circuit 470, 472, or 474) reaches a hightemperature and the upper limit travelling speed is thus reduced, theupper limit travelling speed is not set back to its original speedunless the cart 2 is stopped, even if the operation mode of the cart isnot the automatic mode. Thus, the cart 2 can be suppressed from suddenlyaccelerating.

In one or more embodiments, after the upper limit travelling speed hasbeen changed from the first upper limit travelling speed to the secondupper limit travelling speed, the main MCU 434 is configured to set theupper limit travelling speed back to the first upper limit travellingspeed if the cart 2 is stopped.

If the cart 2 is not stopped upon setting the upper limit travellingspeed back to the first upper limit travelling speed from the secondupper limit travelling speed, there is a risk that the cart 2 suddenlyaccelerates. According to the above configuration, after the brakecircuit 468 (or the brake circuit 470, 472, or 474) reaches a hightemperature and the upper limit travelling speed is thus reduced, theupper limit travelling speed is not set back to its original speed untilthe cart 2 is stopped, thus the cart 2 can be suppressed from suddenlyaccelerating.

In one or more embodiments, the cart 2 further comprises: the left frontwheel 212 (or the right rear wheel 252, the left rear wheel 272, or theright front wheel 192) (examples of second driving wheel); the leftfront wheel motor 242 (or the right rear wheel motor 486, the left rearwheel motor 492, or the right front wheel motor 232) (examples of secondmotor) configured to rotate the left front wheel 212 (or the right rearwheel 252, the left rear wheel 272, or the right front wheel 192); themotor driver 456 (or the motor driver 458, 460, or 454) (examples ofsecond motor drive circuit) configured to drive the left front wheelmotor 242 (or the right rear wheel motor 486, the left rear wheel motor492, or the right front wheel motor 232); the brake circuit 470 (or thebrake circuit 472, 474, or 468) (examples of second motor brake circuit)configured to electrically brake the left front wheel motor 242 (or theright rear wheel motor 486, the left rear wheel motor 492, or the rightfront wheel motor 232); and the thermistor 470 e (or the thermistor 472e, 474 e, or 468 e) (examples of second temperature sensor) configuredto detect the temperature of the brake circuit 470 (or the brake circuit472, 474, or 468). The main MCU 434 and the motor MCU 444, 446, 448, or450 are configured to control the left front wheel motor 242 (or theright rear wheel motor 486, the left rear wheel motor 492, or the rightfront wheel motor 232) via the motor driver 456 (or the motor driver458, 460, 454) and the brake circuit 470 (or the brake circuit 472, 474,or 468) so that the travelling speed of the cart 2 becomes equal to orlower than the upper limit travelling speed. When the temperaturedetected by the thermistor 470 e (or thermistor 472 e, 474 e, or 468 e)exceeds the temperature protection threshold T1, the main MCU 434 isconfigured to change the upper limit travelling speed to the secondupper limit travelling speed also.

According to the above configuration, when one of the brake circuit 468(or the brake circuit 470, 472, or 474) and the brake circuit 470 (orthe brake circuit 472, 474, or 468) exceeds the temperature protectionthreshold T1, the heat quantities in the brake circuit 468 (or the brakecircuit 470, 472, or 474) and the brake circuit 470 (or the brakecircuit 472, 474, or 468) that are generated upon braking the rightfront wheel motor 232 (or the left front wheel motor 242, the right rearwheel motor 486, or the left rear wheel motor 492) and the left frontwheel motor 242 (or the right rear wheel motor 486, the left rear wheelmotor 492, or the right front wheel motor 232) can be reduced byreducing the upper limit travelling speed of the cart 2 from the firstupper limit travelling speed to the second upper limit travelling speed.The brake circuit 468 (or the brake circuit 470, 472, or 474) and thebrake circuit 470 (or the brake circuit 472, 474, or 468) can besuppressed from reaching excessively high temperatures.

In one or more embodiments, the cart 2 further comprises the cooling fan50 d (or the cooling fan 52 d, 54 d, or 56 d) (examples of cooler)configured to cool the brake circuit 468 (or the brake circuit 470, 472,or 474). The cooling fan 50 d (or the cooling fan 52 d, 54 d, or 56 d)is configured to continue cooling the brake circuit 468 (or the brakecircuit 470, 472, or 474) even after the right front wheel motor 232 (orthe left front wheel motor 242, the right rear wheel motor 486, or theleft rear wheel motor 492) has stopped.

According to the above configuration, since the brake circuit 468 (orthe brake circuit 470, 472, or 474) can be cooled by the cooling fan 50d (or the cooling fan 52 d, 54 d, or 56 d) even while the right frontwheel motor 232 (or the left front wheel motor 242, the right rear wheelmotor 486, or the left rear wheel motor 492) is stopped, the brakecircuit 468 (or the brake circuit 470, 472, or 474) can be cooledsufficiently, by which the brake circuit 468 (or the brake circuit 470,472, or 474) can be suppressed from reaching excessively hightemperatures when the cart 2 operates thereafter.

In one or more embodiments, the brake circuit 468 (or the brake circuit470, 472, or 474) is configured to electrically brake the right frontwheel motor 232 (or the left front wheel motor 242, the right rear wheelmotor 486, or the left rear wheel motor 492) for 15 minutes or more.

According to the above configuration, braking on the right front wheelmotor 232 (or the left front wheel motor 242, the right rear wheel motor486, or the left rear wheel motor 492) by the brake circuit 468 (or thebrake circuit 470, 472, or 474) can be continued over a long period oftime, and the operation of the cart 2 can further be stabilized.

In one or more embodiments, the upper limit travelling speed is within arange from 0 km/h to 10 km/h.

According to the above configuration, the cart 2 can be suppressed fromtravelling at an excessively high speed, and travelling safety for thecart 2 can be increased.

What is claimed is:
 1. A cart comprising: a driving wheel; a motorconfigured to rotate the driving wheel; a motor drive circuit configuredto drive the motor; a motor brake electronic circuit configured toelectrically brake the motor; a control device configured to control themotor via the motor drive circuit and the motor brake electronic circuitso that a travelling speed of the cart becomes equal to or lower than anupper limit travelling speed; and a temperature sensor configured todetect a temperature of the motor brake electronic circuit, wherein whenthe upper limit travelling speed is a first upper limit travelling speedand the temperature detected by the temperature sensor exceeds a firstpredetermined temperature, the control device is configured to changethe upper limit travelling speed to a second upper limit travellingspeed lower than the first upper limit travelling speed.
 2. The cartaccording to claim 1, wherein, when the temperature detected by thetemperature sensor becomes lower than a second predetermined temperaturelower than the first predetermined temperature after the upper limittravelling speed has been changed from the first upper limit travellingspeed to the second upper limit travelling speed, the control device isconfigured to set the upper limit travelling speed back to the firstupper limit travelling speed.
 3. The cart according to claim 2, furthercomprising an operation member for receiving an operation by a user,wherein the cart is configured to operate in a manual mode and anautomatic mode, and the control device is configured such that: in themanual mode, the motor is driven when the operation member is on and themotor is stopped when the operation member is off, and, in the automaticmode, the motor is driven regardless of whether the operation member ison or off, and the upper limit travelling speed is not set back to thefirst upper limit travelling speed if the cart is in the automatic modewhen the temperature detected by the temperature sensor becomes lowerthan the second predetermined temperature after the upper limittravelling speed has been changed from the first upper limit travellingspeed to the second upper limit travelling speed.
 4. The cart accordingto claim 3, wherein, when the temperature detected by the temperaturesensor becomes lower than the second predetermined temperature and thecart is not in the automatic mode after the upper limit travelling speedhas been changed from the first upper limit travelling speed to thesecond upper limit travelling speed, the control device is configurednot to set the upper limit travelling speed back to the first upperlimit travelling speed if the cart is not stopped.
 5. The cart accordingto claim 4, further comprising: a second driving wheel; a second motorconfigured to rotate the second driving wheel; a second motor drivecircuit configured to drive the second motor; a second motor brakeelectronic circuit configured to electrically brake the second motor; asecond temperature sensor configured to detect a temperature of thesecond motor brake electronic circuit; and a cooler configured to coolthe motor brake electronic circuit, wherein the control device isconfigured to control the second motor via the second motor drivecircuit and the second motor brake electronic circuit so that atravelling speed of the cart becomes equal to or lower than the upperlimit travelling speed, when the upper limit travelling speed is thefirst upper limit travelling speed and the temperature detected by thesecond temperature sensor exceeds the first predetermined temperature,the control device is configured to change the upper limit travellingspeed to the second upper limit travelling speed, the cooler isconfigured to continue cooling the motor brake electronic circuit afterthe motor has stopped, the motor brake electronic circuit is configuredto electrically brake the motor for 15 minutes or more, and the upperlimit travelling speed is within a range from 0 km/h to 10 km/h.
 6. Thecart according to claim 2, wherein, when the temperature detected by thetemperature sensor becomes lower than the second predeterminedtemperature after the upper limit travelling speed has been changed fromthe first upper limit travelling speed to the second upper limittravelling speed, the control device is configured not to set the upperlimit travelling speed back to the first upper limit travelling speed ifthe cart is not stopped.
 7. The cart according to claim 1, furthercomprising an operation member for receiving an operation by a user,wherein the cart is configured to operate in a manual mode and anautomatic mode, and the control device is configured such that: in themanual mode, the motor is driven when the operation member is on and themotor is stopped when the operation member is off, and, in the automaticmode, the motor is driven regardless of whether the operation member ison or off, and the upper limit travelling speed is set back to the firstupper limit travelling speed if the cart is not in the automatic modeafter the upper limit travelling speed has been changed from the firstupper limit travelling speed to the second upper limit travelling speed.8. The cart according to claim 7, wherein, when the cart is not in theautomatic mode after the upper limit travelling speed has been changedfrom the first upper limit travelling speed to the second upper limittravelling speed, the control device is configured not to set the upperlimit travelling speed back to the first upper limit travelling speed ifthe cart is not stopped.
 9. The cart according to claim 1, wherein afterthe upper limit travelling speed has been changed from the first upperlimit travelling speed to the second upper limit travelling speed, thecontrol device is configured to set the upper limit travelling speedback to the first upper limit travelling speed if the cart is stopped.10. The cart according to claim 1, further comprising: a second drivingwheel; a second motor configured to rotate the second driving wheel; asecond motor drive circuit configured to drive the second motor; asecond motor brake electronic circuit configured to electrically brakethe second motor; and a second temperature sensor configured to detect atemperature of the second motor brake electronic circuit, wherein thecontrol device is configured to control the second motor via the secondmotor drive circuit and the second motor brake electronic circuit sothat a travelling speed of the cart becomes equal to or lower than theupper limit travelling speed, and when the upper limit travelling speedis the first upper limit travelling speed and the temperature detectedby the second temperature sensor exceeds the first predeterminedtemperature, the control device is configured to change the upper limittravelling speed to the second upper limit travelling speed.
 11. Thecart according to claim 1, further comprising a cooler configured tocool the motor brake electronic circuit, wherein the cooler isconfigured to continue cooling the motor brake electronic circuit afterthe motor has stopped.
 12. The cart according to claim 1, wherein themotor brake electronic circuit is configured to electrically brake themotor for 15 minutes or more.
 13. The cart according to claim 1, whereinthe upper limit travelling speed is within a range from 0 km/h to 10km/h.